BACKGROUND The treatment of Tourette's disorder with classical neuroleptics is limited by their side effects. Risperidone is a new efficacious antipsychotic with a low propensity for extrapyramidal side effects. To establish risperidone's therapeutic potential in Tourette's disorder, we studied the safety and efficacy of risperidone in comparison with pimozide in patients with Tourette's disorder diagnosed according to DSM-III-R. METHODS In a 12-week, multicenter, double-blind, parallel-group study, 26 patients were treated with risperidone (mean daily dose = 3.8 mg), and 24 patients were treated with pimozide (mean daily dose = 2.9 mg). RESULTS There was significant improvement of tics with respect to the Tourette's Symptom Severity Scale (TSSS) for both groups. Forty-one patients completed the study. At endpoint, 54% (14/26) of the risperidone patients and 38% (9/24) of the pimozide patients had only very mild or no symptoms on the global severity rating of the TSSS. Both treatment groups had improved significantly at endpoint in regard to Global Assessment of Functioning and Clinical Global Impressions scale outcomes. Symptoms of anxiety and depressive mood improved significantly from baseline in both groups. Obsessive-compulsive behavior improvement reached significance only in the risperidone group. Although the severity of extrapyramidal side effects was low in both groups, fewer patients in the risperidone group reported extrapyramidal side effects (N = 4) compared with the pimozide group (N = 8). Depression, fatigue, and somnolence were reported as the most prominent side effects in both treatment groups. CONCLUSIONS Both drugs were efficacious and well tolerated in patients with Tourette's disorder. Risperidone may become the first-line drug in the treatment of Tourette's disorder owing to a more favorable efficacy and tolerability profile.