A growing number of states are passing laws requiring health insurers to cover children under their parents' plans well into adulthood.

Most group or private health-insurance plans end eligibility for dependents when a child turns 19. The age limit is extended for full-time students, but still generally tops out at about 22 or 23. Now, at least 22 states have recently passed laws, or are considering legislation, that require insurers to offer coverage to even older dependents, often whether they are in school or not. Although adding an adult dependent could raise the premium that a family must pay, lawmakers expect the added cost would be less than if the dependent purchased a separate policy.

In New Jersey, a law taking effect next month requires health insurers to cover single adult dependents until the age of 30. The law applies to most group health plans, which employees typically receive through their work. A law in Colorado that went into effect in January mandates that dependents be covered until they turn 25. Lawmakers in that state are now considering a bill that would further extend coverage to an adult dependent's minor children. New Mexico, Utah and Massachusetts have enacted laws along the same lines, while other states are considering similar legislation, according to the National Conference of State Legislatures.

Policy analysts say lawmakers are concerned about the growing cost of picking up the tab for some of the nation's 46 million people that aren't covered by health insurance. In recent years, young adults, from 19 to 34 years old, were the fastest growing group of uninsured, according to a recent study by the Kaiser Family Foundation, a health-care policy research group. The federal and state governments spent an estimated $41 billion in 2004 on so-called uncompensated medical care, including paying hospitals for treating uninsured patients, according to a national health-care survey.

Some employers and business groups say the measures will drive up the cost of health insurance for everyone and may force more employers to stop offering it. A survey by the Kaiser foundation found that 60 percent of companies offered health insurance to their workers last year, down from 69 percent in 2000. The majority of survey respondents that don't offer coverage cited cost as a key factor. Health-care premiums rose an average 9 percent last year and were up 11 percent in 2004, according to the foundation.

Some observers have mocked the trend as another example of the younger generation's difficulty leaving the nest, a cultural phenomenon so widespread as to have spawned its own hit film, "Failure to Launch," and at least one TV series, Fox's "Free Ride." One factor: With college-tuition costs soaring, the average student graduated earlier this decade with more than $19,000 in debt, adjusted for inflation, up from about $12,000 in the early 1990s, according to the National Center for Education Statistics.

Kaiser Foundation Health Plan of Colorado, which provides health insurance for 460,000 Colorado residents, opposed the bill because it "attempts to broaden coverage by shifting the burden to employers," says Leo Tokar, vice president of marketing. The company is passing along to its customers a 1 percent premium increase to cover the additional costs stemming from that state's new law, he says. Kaiser customers expect their costs to go up, in turn. Coors Brewing Co., a subsidiary of Molson Coors Brewing Co., says the measure would add $300,000 to the annual premiums the company pays for its 3,000 Colorado employees. Aerospace giant Lockheed Martin Corp. also says it expects higher health-care costs. Lockheed is based in Bethesda, Md., but runs several operations in Colorado that employ 8,000 people.

The Colorado law, which applies both to group and privately purchased individual health plans, requires insurers to offer a parent continuing coverage for an unmarried child who is under 25. Insurers have the option to charge an additional premium. The child must live at the same address as the parent, or be financially dependent. But financial dependency isn't defined by the statute, nor is the premium that employers can charge. The law doesn't apply to federal employee plans or plans that are self-funded by an employer.

Colorado State Sen. Brandon Shaffer, who co-sponsored the law, said the target population was part-time students and young working adults who still rely on their parents for financial support. Nearly 40 percent of the state's uninsured were 18 to 34 years old in 2004, according to the Colorado Health Institute, an independent research group. The figure is in line with the national average.

The New Jersey law provides for dependents to be covered up to the age of 30, but allows insurers to charge a separate premium for these older dependents. State Assemblyman Neil Cohen, who sponsored the bill, estimates the additional coverage could cost an average family between $2,500 and $3,000 a year, well below the roughly $7,000 cost of an individual policy in the state. Some critics say his cost estimate is unrealistically low. Mr. Cohen said he expects 100,000 to 200,000 young people would find coverage under the new law.

Several states are considering similar bills. A Rhode Island bill would phase in coverage of older dependent children over several years, raising the age limit to 21 in 2007, 23 in 2008, and 25 as of 2009. Dependents would have to be unmarried and financially dependent to qualify, but they wouldn't have to be enrolled in higher education. In Massachusetts, a bill awaiting the governor's signature states that dependents are eligible for coverage until their 25th birthday, or two years after their parents no longer claim them on their tax returns, whichever comes first. The bill is part of a comprehensive health-insurance package that requires every individual in the state to obtain coverage.

Some states' legislation is narrowly crafted to address specific problems. In New Hampshire, a bill would require insurers to continue coverage for full-time students who have to take a medical leave of absence due to illness or injury. A Pennsylvania law enacted last year states that full-time students whose studies were interrupted by National Guard or armed-forces reserve duty must be allowed extended health-care benefits until they finish school, regardless of their age.

At least four states, including New York and Minnesota, currently require health plans to cover grandchildren if they are financially supported by the grandparent or are in their legal custody. In Texas, a grandchild who is a legal dependent must be covered until his 25th birthday as long as he or she remains unmarried. Coverage can't be terminated even if the child is no longer a dependent for tax purposes, according to the National Conference of State Legislatures.

To determine if extended dependent coverage is the best choice, parents should compare it against an individual health-care policy or the federally mandated Consolidated Omnibus Budget Reconciliation Act, or Cobra. Adult children are allowed to sign up for Cobra when their eligibility ends under their family's plan. Cobra is most often used to provide continuing health-care coverage when an employee leaves his or her job. Under Cobra, continuing group coverage is available for a maximum 36 months, but requires the individual to pay the full premium cost under the health plan plus an administrative fee of 2 percent. In 2005, the average annual premium for individual coverage under a group policy was $4,024, according to a national survey.

Forever Young

Some states are allowing adult children to stay covered by their parents' health-insurance policies for a longer time.

Young adults are the fastest growing segment of the uninsured population.

Many state laws extend coverage regardless of whether the child is a full-time student.

Premiums could go up, but increases should be less than purchasing a separate policy.

Older Dependents

Several states have passed or are considering laws that require insurers to extend coverage for adult dependents of health-insurance beneficiaries.

New Jersey: A law that takes effect in May states that a dependent may be covered up to his 30th birthday, so long as he has no dependents of his own.

Colorado: Effective Jan. 1st, a law states that a child can be considered a dependent for the purpose of health-insurance coverage until his 25th birthday, even if he is not enrolled in an educational institution, as long as he is unmarried and financially dependent, or shares the same address as the covered parent.

New Mexico: Effective July 1, 2005, a law states that health insurance for dependents can't be terminated based on age before the 25th birthday, regardless of whether dependent is enrolled in an educational institution.

Utah: A 1994 law requires that coverage for an unmarried dependent continue until the 26th birthday regardless of whether he is enrolled in an educational institution.

Maine: A bill would require insurance companies to cover dependent children until the age of 24 if they have a mental or physical disability that prevents them from being enrolled in a postsecondary institution.

New Hampshire: A bill would require insurance companies to continue coverage for dependents who would have aged out of their insurance coverage, if they are mentally or physically incapable of earning a living. Coverage would continue as long as the incapacity continues.

Source: National Conference of State Legislatures; states.