In just the past few years, researchers have identified what they believe is an adult version of attention deficit disorder: a restless inability to concentrate that develops spontaneously after high school, years after the syndrome typically shows itself, and without any early signs.

The proposed diagnosis — called adult-onset A.D.H.D. and potentially applicable to millions of people in their late teenage years or older — is distinct from the usual adult variety, in which symptoms linger from childhood. Yet a new study suggests that adult-onset A.D.H.D. is rare, if it exists at all.

The authors of the new report, led by Margaret Sibley, an associate professor of psychiatry and behavioral health at Florida International University, carefully examined the extensive records of those 24 with adult-onset A.D.H.D. The researchers found that the attention deficits in all but five cases most likely stemmed from other causes, like marijuana use, depression or anxiety.

Read the full article by The New York Times about the study on adult-onset A.D.H.D.