An association of obstructive sleep apnea syndrome (OSAS) and other sleep-disordered breathing (SDB) with Parkinson's disease (PD) has been reported in some small studies. In the present study we investigated the occurrence of SDB in a large consecutive outpatient series. This is a case-control study in subjects attending a neurological clinic where all patients were screened for SDB by means of sleep-wake history, Epworth Sleepiness Scale, and full-night polysomnography, when indicated. 3194 patients were recruited. Of these, 194 were affected by PD and 77 by other parkinsonisms. Snoring, excessive daytime sleepiness and OSAS were more common in patients with PD or parkinsonisms (40.59, 5.9, and 4.06%) than in controls (35.58, 2.19, and 2.09%). Our study suggests an increased frequency of OSAS and other SDB in PD and parkinsonisms. Early detection and management of these disorders may have a substantial impact on quality of life and survival in these patients.