LUXEMBOURG -- Young Leonhard Matthias Grunkin-Paul has a problem: His name is illegal.

The German boy's divorced parents want Leonhard to be known by their combined last names, an increasingly common practice elsewhere. But authorities in Germany, citing a law against hyphens, have refused to allow it. So Leonhard, born in 1998, officially has no last name at all.

His passport reads: "Leonhard Matthias, son of Stefan Grunkin and Dorothee Paul." Says his mother: "I don't know how he can go through life like that."

Many Germans have long chafed under their country's rigid naming rules. But a European Union court may shortly deal the rules a blow for at least some of them. A preliminary ruling from the court has found that Leonhard, a German citizen born and named in Denmark, is entitled to his hyphen as a citizen of the EU.

In a society that values order and tradition, the rules are meant to prevent German children from being the victims of ridicule or confusion. A forename must indicate a person's gender, for example; if it doesn't, a second name should be given that clarifies the matter.

"We have had these rules for as long as I can remember," says Karin M. Eichhoff-Cyrus, director of the state-funded German Language Society, which helps enforce the rules. "Everyone knows you cannot have a name that is 'Refrigerator' or something."

And why no hyphens? Dr. Eichhoff-Cyrus, who hyphenated her own surname after marriage but is not allowed to pass it on to her children, explains that the concern is hyphenation multiplication. If a double-named boy grew up to marry and have children with a double-named woman, those children could have four names, and their children could have eight, and their children could have 16. The bureaucracy shudders.

All Germans register their names with the Standesamt, or local registry. Standards vary from place to place, and applicants who are turned down can appeal to the courts. Authorities are usually more flexible about first names than last. Among the first names approved over the years, according to the Language Society: Pumuckl, taken from a cartoon character, and Pepsi-Carola, taken from a soft drink. Rejected: Lenin, McDonald, Schnucki and Bierstubl, which translates roughly as "little beer pub."

A Dusseldorf court in 1998 rejected the name Chenekwahow Migiskau Nikapi-Hun-Nizeo Alessandro Majim Chayara Inti Ernesto Prithibi Kioma Pathar Henriko, on the grounds that the mother's wish to honor multiculturalism shouldn't result in an awkwardly long name for the child. A Frankfurt court upheld the name Jesus the same year, in part because it's widely known that Christ was male, leaving little room for gender confusion.

Germany isn't alone in Europe in regulating names. Slovakia, for example, forbids first names that are eccentric, derogatory or ludicrous (parents can't name a child "Cigarette," for instance). It also generally bans hyphenated last names for children -- though the Ministry of Interior says it makes an exception for the children of hyphenated foreigners living in Slovakia. Natives are allowed double surnames without hyphens.

But in Belgium, authorities in 1997 told children of a Spanish-Belgian marriage they could not switch to a Spanish-style double surname: "There are insufficient grounds to propose to His Majesty the King that he grant you the favor of changing your surname." They appealed to an EU court and won. The United Kingdom, on the other hand, imposes almost no rules.

In Germany, the Language Society helps navigate the minefield, responding to several thousand requests each year from residents seeking guidance on names before they go to the Standesamt. Increasingly these requests come from people of Asian, African or Middle Eastern origin who must prove they're not trying to slip, say, the Chinese equivalent of Moon Unit Zappa past unsuspecting German authorities.

Drawing on branches in 20 countries, the society researches non-German names for conformance to the German rules. The name must be in use in its country of origin, for example. One indicator: people by that name appear in books or newspapers. The society also confirms the name's gender association. Then it compiles its findings in an opinion that an applicant can present to the registrar. "Our opinions are almost never rejected," Dr. Eichhoff-Cyrus says.

Recently the society advised a couple that authorities probably wouldn't allow them to name their daughter Chanel. "It sounds very pretty, but still, it's a brand name," Dr. Eichhoff-Cyrus says. There are times that German authorities permit people to change their given name. A Munich court allowed a man to ditch "Adolf" because it made people think of Hitler. Courts also recognize the right of transsexuals to change their honorific -- "Frau" to "Herr," or vice versa.

Leonhard's case is helped by his living with his mother in Denmark, an EU country more tolerant of hyphens. That puts it in the purview of the EU court, and raises the question of whether one EU member nation can legally uphold restrictions on citizens, given that they're free to move to other EU nations where the restrictions don't apply.

And so in April, Leonhard's father took an overnight train from Hamburg to the tiny duchy of Luxembourg, seat of the EU court to which his local municipal court in Germany had referred the hyphen case. Before a panel of crimson-robed judges, Mr. Grunkin told his domestic story: His wife, Dr. Paul, kept her maiden name after their marriage. Leonhard was born in Denmark. The couple was divorced in 2003, and Leonhard and his mother stayed in Denmark, where she practices medicine and he lives legally with his hyphenated name.

All three remain German citizens, Mr. Grunkin explained. But now, when his son travels a dozen miles over the border into Germany to stay with him, the boy suddenly has no official last name. German authorities suggested the boy simply remove the offending hyphen. But Mr. Grunkin argued that would downgrade his own legacy to just another of his son's middle names. "I am the child's father!" he said. "But they say the child has to accept a different name in Germany, the name of the mother?"

He pleaded with the court: "My ex-wife and I made a deliberate choice to give the child a hyphenated name. It's simply untenable that the German authorities want to dig their heels in on this point."

A lawyer for the German government, Alfred Dittrich, countered: "The problem is the parents decided to choose a name that they knew, or must have known, was illegal in Germany."

Mr. Grunkin sighed and rolled his eyes.

Two months after the hearing, Mr. Grunkin received some vindication. The court's advisory opinion, usually a good indicator of how the judges will eventually rule, called Germany's rejection of the hyphen "totally incompatible" with Leonhard's rights as an EU citizen. A final decision is expected by the end of the year.