Harry Potter has cast a spell on many young readers, but J.K. Rowling's latest book in the series has inflicted some fans with a dull ache in the noggin.

Call it Hogwarts headache.

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In a letter published in today's New England Journal of Medicine, Dr. Howard J. Bennett, a pediatrician in Washington, D.C., describes generalized headaches suffered in the past several months by three of his patients, who range in age from 8 to 10.

Each complained about headaches that persisted for two or three days, yet Bennett found the children were reasonably healthy, with no infections or neurological problems that might explain prolonged headaches.

But in talking further with each child, Bennett learned that each had been spending long hours plowing through "Harry Potter and the Order of the Phoenix," the tome that was published over the summer.

Four earlier books in the series apparently didn't spawn headaches, Bennett said, but at 870 pages and about 3 pounds, the fifth book requires more mental and physical effort of its readers than Professor Snape's classes at the Hogwarts School of Witchcraft and Wizardry.

Two of his patients would lie prone to read the bulky book, while the other propped the book on her legs and rested her head on a pillow so she could keep reading.

Hogwarts headache is the latest in a long medical journal tradition of lighthearted reports on the hazards of everyday living. These have included such ailments as Frisbee finger, cuts on the finger caused by strenuous throwing of a Frisbee; Nintendinitis, thumb tendon inflammation from playing video games; and disco digit, a sore finger from snapping the fingers while dancing.

"It's not a spoof," Bennett said of the letter, "but it's not meant to be overwhelmingly deep."

Certainly, no one can say that this is any sort of epidemic.

"We have not encountered anything like that," said Dr. Inna Vaisleib, a pediatric neurologist at Children's Hospital and one of two neurologists in its headache clinic. Then again, a headache that lasts only a few days without other symptoms is not likely to be referred to a specialty clinic, which primarily treats children with migraine headaches.

But Bennett said that in his pediatric practice, "we see headaches all the time." Many schoolchildren suffer headaches at the end of the school day, he said, a sign of fatigue similar to what the Hogwarts headache sufferers reported.

The muscles of the eye can indeed get tired after too much reading, causing a dull ache, Vaisleib said. Also, if a page-turner like the Harry Potter book keeps children up past their regular bedtimes, sleep deprivation can cause or contribute to the ache.

Muggle (non-magical) though he may be, Bennett wrote the letter in hopes that doctors might pay more attention to headache complaints, not to criticize the Potter books.

"I'm a fan of Rowling's," he said. "I want kids to keep reading the books, to keep reading books in general."

To avoid headaches, however, they should take breaks now and then and consider reading at a desk with proper lighting.

Two of his patients rejected that advice, opting to use acetaminophen to dull the ache so they could go right on reading. Ultimately, the headaches ended within a day or two after each child finished the book.

But in a tongue-in-cheek conclusion to his letter, Bennett observed that each successive Potter book has grown in length and weight, an ominous trend.

"If this escalation continues as Rowling concludes the saga, there may be an epidemic of Hogwarts headaches for years to come."