BACKGROUND: Sleep disturbances are very common in the patients with Parkinson's disease (PD) and several sleep disorders are known to have pathological associations with PD, such as REM sleep behavior disorder (RBD), restless legs syndrome (RLS) and periodic limb movement disorder (PLMD). The authors conducted this study to find clinical characteristics and impact of sleep disorders in the patients with PD. METHODS: A total of 97 patients with PD (41 males, age 61.0+/-9.3 years, Hoehn and Yahr stage 1-4) were recruited. We interviewed bed partners of parkinsonian patients for sleep disorders with structured questionnaires and compared interview results with the clinical characteristics of Parkinson's disease and the results of cognitive function tests. RESULTS: RLS (24.7%), RBD (19.6%), sleep apnea (15.5%) and PLMD (13.4%) were frequently reported by bed partners of the patients. PLMD, RBD and apnea were significantly increased in male patients. Parkinsonian characteristics of the patients (dose of L-dopa, predominant motor symptom, duration of symptom and treatment, use of dopamine agonist, Hoehn and Yahr stage, and severity of motor symptoms) were not related with sleep disorders and daytime sleepiness, but the bed partners reported decreased arousal and increased daytime sleepiness in the patients with sleep disorders. The cognitive profiles of the patients showed impaired memory function in the sleepy patients. CONCLUSIONS: We could not find the correlations between sleep disorders and the clinical characteristics of PD. But, sleep disorders were prevalent in PD patients and caused daytime sleepiness and cognitive dysfunctions.