Parents and advocates have been clamoring for an approach that addresses the multiple health problems that plague many children with autism. “Our kids will do much better if medical conditions like gut issues or allergies are treated,” said Lee Grossman, president of the Autism Society of America, a leading advocacy group.

The new diagnostic approach addresses another source of confusion: the current labels may change over time. “A child can look like they have P.D.D.-N.O.S., then Asperger’s, then back to autism,” Dr. Lord said. The inconsistent use of these labels has been a problem for researchers recruiting subjects for studies of autism spectrum disorder.

And it can be a problem for people seeking help. In some states, California and Texas, for example, people with traditional autistic disorder qualify for state services, while those with Asperger’s and pervasive developmental disorder do not.

A big challenge for the diagnostic manual team working on autism is how to measure severity in a condition that often causes a very uneven profile of abilities and disabilities. Mr. Grossman gives the example of a woman who serves on an advisory panel to his organization. She is nonverbal and depends on an electronic device to communicate, is prone to self-injury and relies on a personal aide. And yet “she’s absolutely brilliant, she runs a newsletter, and she’s up on all the science,” he said, adding, “Where would somebody like that come out on the rating scale?”

Recent books by people with Asperger’s give insights into the workings of some oddly beautiful minds. In “Embracing the Wide Sky” (Free Press, 2009), Daniel Tammet, a shy British math and linguistic savant, tells how he was able to learn enough Icelandic in a week to manage a television interview and how he could recite the value of pi to 22,514 decimal places by envisioning the digits “as a rolling numerical panorama” of colors, shapes and textures.

In “Look Me in the Eye” (Crown, 2007), John Elder Robison describes a painfully lonely childhood and an ability to look at a circuit design and imagine how it will transform sound  a talent he used to invent audio effects and exploding guitars for the rock band Kiss.

Not all people with Asperger’s have such extraordinary abilities, and some who do are so crippled by anxiety and social limitations that they cannot hold down a job or live on their own.