The validity of several DSM-III diagnoses remains controversial. Studies are underway across several centers addressing the validity of the diagnostic distinction between situational and cross situational hyperactivity, and between obsessive compulsive disorder (OCD), subclinical OCD, and compulsive personality disorder. In the U.K., great emphasis is placed upon cross situational hyperactivity (based on parent and teacher behavior ratings). This distinction will be validated using 24-hour motor activity measure for hyperactive children and controls in London and Washington. The validity of the distinction between OCD, subclinical OCD, OCP is being assessed with: studies of interrater reliability, associated features and family studies, and follow-up status.