Fifty patients with Tourette syndrome were evaluated; data included family history, clinical characteristics, response to haloperidol, and side effects during haloperidol therapy. Sixteen patients had a family history of Tourette syndrome, and another 16 had a family history of tics. Twenty-four families had more than 2 members with Tourette syndrome or tics. There was no preponderance of families with a Jewish, Eastern European background in this sample. Thirty-four patients had obsessive-compulsive behavior. Among the 50 patients there was a high frequency of sleep disturbance, learning disability, self-destructive behavior, inappropriate sexual activity, and antisocial behavior. Family history was significantly related to the occurrence of sleep disturbance, obsessive-compulsive behavior, haloperidol response, and the frequency of side effects caused by haloperidol. The precise mode of genetic transmission in familial Tourette syndrome remains to be determined.