Quetiapine is an atypical antipsychotic with sedative properties frequently used to treat hallucinations and psychosis in Parkinson disease (PD). The objective of this trial is to evaluate quetiapine for insomnia in nonpsychotic PD patients. Fourteen consecutive PD patients with frequent insomnia and without psychotic symptoms were treated openly for 12 weeks with a single evening dose of quetiapine. The dose was adjusted according to clinical improvement and tolerance. The severity of insomnia was assessed using the Pittsburgh Sleep Quality Index (PSQI), daytime sleepiness was evaluated with the Epworth Sleep Scale (ESS), and motor performance was evaluated using the motor section of the Unified Parkinson's Disease Rating Scale (UPDRS). All evaluations were done before and 1, 2, and 3 months after initiation of treatment. Total PSQI basal scores were 13.6 +/- 3.7 points. The PSQI score improved in 11 patients and was reduced by 3.8 +/- 3.9 points by the end of the study (P < 0.01). The ESS score was reduced by 4.3 +/- 3.7 points (P < 0.01). The mean quetiapine dose was 31.9 mg/day. No significant change was observed in the motor scale. Two patients were discontinued due to nonserious adverse effects. These results suggest that quetiapine may be a safe and effective treatment of insomnia in PD patients. Double-blind studies will probably confirm these findings.