Aripiprazole is an agent for treating schizophrenia. The authors assume that aripiprazole as a dopamine receptor partial agonist may be useful in treating PD patients. Three cases are presented in this study. All patients were evaluated by the same clinician, a neuropsychiatrist well trained in the use of Brief Psychiatric Rating Scale (BPRS) and Clinical Global Impression (CGI). Aripiprazole was effective for reducing psychosis in each case.