Though both psychosis and depression are common in Parkinson's disease (PD), it is not clear if an association between the two disorders exists. One hundred and thirty PD patients were divided into four groups based on a comprehensive psychiatric assessment: (1) no depression or psychosis (47.7%); (2) psychosis only (16.2%); (3) depression only (26.2%); and (4) psychosis and depression (10.0%). Co-morbid psychosis and depression did not occur more frequently than expected by chance (P=.77). Psychosis was associated with dopamine agonist use (P=.02), depression with mild-cognitive impairment (P=.03), and their co-occurrence with higher daily levodopa dosages (P<.01). These results suggest that psychosis and depression in PD are distinct neurobehavioral disorders.