We describe a long-term follow-up study (1-15 years) of 33 patients with Tourette syndrome who were treated with pimozide (2-18 mg), haloperidol (2-15 mg), or no drugs. Both drugs produced comparable relief of symptoms at follow up; however, significantly more patients on haloperidol (eight of 17), compared with those on pimozide (one of 13), discontinued treatment (p less than or equal to 0.05). Haloperidol produced significantly more acute dyskinesias/dystonias than pimozide (p less than or equal to 0.03); otherwise, the adverse effect profile was similar for the two drugs. In particular, we found no increased incidence of ECG abnormalities in patients treated with pimozide. A prospective, randomized, double-blind crossover trial is required to determine whether there are significant differences in efficacy between pimozide and haloperidol in treatment of Tourette's disorder.