Sleep disorders are common and well documented in patients with Parkinson's disease (PD). However, most data on sleep in patients with PD are derived from selected patient populations. This community-based survey evaluated the prevalence of and risk factors for sleep disturbances in an unselected group of 245 patients with PD and two control groups of similar age and sex distribution: 100 patients with another chronic disease (diabetes mellitus) and 100 healthy elderly persons. Nearly two thirds of the patients with PD reported sleep disorders, significantly more than among patients with diabetes (46%) and healthy control subjects (33%). About a third of the patients with PD rated their overall nighttime problem as moderate to severe. The most common sleep disorders reported by the patients with PD were frequent awakening (sleep fragmentation) and early awakening. Sleep initiation showed no significant difference compared with the control groups. Pain and cramps were not more prevalent among the patients with PD, but they were more likely to report sleep disturbed by myoclonic jerks. Use of sedatives was common in all three groups but significantly higher in the PD group than in the healthy elderly. Symptoms of depression and duration of levodopa treatment showed a significant correlation with sleep disorders in the PD group. This community-based study confirms that sleep disorders are common and distressing in patients with PD. The strong correlation between depression and sleep disorders in patients with PD underlines the importance of identifying and treating both conditions in these patients.