Sleep attacks in Parkinson's disease are controversially discussed. This paper describes a patient with Parkinson's disease suffering from sudden, irresistible onset of sleep during daytime. Medication included levodopa, entacapone, budipine, and cabergoline. Introduction of entacapone was the last therapeutic action preceding onset of sleep events, suggesting increased bioavailabilty of levodopa to be provocative in this case. In contrast to previous cases, the sudden sleep events were witnessed by clinical staff members and documented by polysomnographic and video recordings. Polysomnography during these sleep events remarkably showed abrupt slowing of EEG-background activity and occurrence of slow eye movements and K-complexes within 10 seconds after stable wakefulness. Within 60 seconds, the polysomnographic pattern proceeded to stable sleep stage 2. © 2001 Movement Disorder Society.