Objectives– Sleep disorders and depression are frequent in patients with Parkinson's disease (PD). However, the exact prevalence and the causality are still unknown. Patients and methods– We interviewed 56 consecutive PD patients and 59 age-matched healthy controls concerning sleep disorders and depression. Sleep Disorders Questionnaire (SDQ) and Zung Depression Scale (ZDS) were used as standardized valid and reliable psychometric tests. Results– Patients with PD had significantly higher values in the clinical-diagnostic scale narcolepsy (P=0.01), correlating with the l-dopa dose (P=0.007). Concerning sleep apnea (P=0.49), psychiatric sleep disorder (P=1.00) and periodic limb movement disorder (P=0.12), no significant difference could be identified. PD patients showed significantly higher depression scores than healthy control subjects (P=0.01), increasing with the duration of PD (P=0.04). Conclusion– The significant higher narcolepsy score in PD patients must be seen due to dopaminergic medication and PD-specific neurodegeneration and immobility rather than due to narcolepsy. This leads to the conclusion that extreme caution is advised when carrying out the SDQ and interpreting the results in various persons and patient groups with motor problems. The strong association of depression, disease severity and sleep disorders in PD patients underlines the importance of identifying and treating both conditions in these patients.