Twelve patients with Parkinson disease and psychosis were included in an open-label 12-week trial of ziprasidone. Two patients withdrew from the treatment because of adverse effects. The remaining 10 patients reported a significant improvement in psychiatric symptoms. Altogether, there was no deterioration of motor symptoms (UPDRS III score: basal 40.4 +/- 11.1, first month 41.1 +/- 10.8; final visit, 37.7 +/- 13.3). Two patients (20%) suffered a slight deterioration in motor symptoms and another patient suffered deterioration of gait. No analytic alterations or serious adverse effects that could limit the use of ziprasidone were observed. Although controlled trials are needed, the findings suggest that ziprasidone may be effective in parkinsonian patients with psychosis.