To determine the prevalence of depression in Parkinson disease (PD) we evaluated 55 consecutive patients without dementia and 31 of their spouses. All subjects completed the Beck depression inventory and a quantitative mini-mental state examination. Using the Beck criteria, 47% of the patients and 12% of the spouses rated themselves as significantly depressed. Mental state scores were significantly lower in the patients. There was a correlation between the severity of depression and cognitive impairment, particularly for calculation, digit span, and visuomotor skills. The severity of parkinsonism, particularly bradykinesia, also paralleled cognition. There was a slight but significant relationship between parkinsonism and depression. These results confirm the high incidence of depression in PD, and suggest that depression in Parkinson patients may be accompanied by mild intellectual impairment and inattention which is independent of the severity of the illness.