This paper reviews the assessment and diagnosis of attention deficit/hyperactivity disorder (ADHD) in adults. To provide baseline information, consideration is given to outcome studies for adults who were first diagnosed with ADHD as children. Studies of clinical assessment methods are addressed, and previous diagnostic criteria are compared to current criteria. Also considered is the area of retrospective childhood diagnosis. The retrospective approach of reviewing childhood symptoms was found to provide moderate agreement between parental and subject recollections of childhood behavior; however, there may be a tendency for subjects to under-report their symptoms compared to parents. Presence of co-morbid disorders such as learning disabilities has confounded much of the clinical assessment of symptomotology. Tests which have been used to differentiate children with ADHD and those with learning disabilities are examined, as are the use of neuropsychological tests in adults. It is concluded that the lack of consensus in the existing literature suggests that a multimodal method of assessment appears necessary at this time. (Contains 39 references.) (SW)