Twenty-two adults who met DSM-III criteria for “Attention Deficit Disorder, Residual Type” (ADD-RT) were evaluated in a series of clinical experiments. Although certain personality and psychological factors typified the ADD-RT group, methylphenidate blood levels, the growth hormone response to methylphenidate, and the brainstem evoked response did not distinguish subjects from matched controls. Male subjects seemed to be a more homogeneous group than female subjects. Socioeconomic status and IQ, but not severity of ADD symptoms, were found to predict outcome. ADD adults seem to be numerous and easy to identify, at least on the basis of symptoms. However, the validity of ADD-RT as a “distinct clinical entity” is open to question.