Currently, it is unclear whether sleep attacks in Parkinson's disease (PD) represent a novel entity or just a phenomenon of daytime sleepiness. We investigated 10 PD patients with sleep attacks and compared them with 10 PD patients without any daytime sleepiness. The patients were matched according to their dopaminergic medication and subjected to a sleep medical investigation. The mean sleep latency on the multiple sleep latency test was in the normal range and not significantly different between the groups. These data suggest that sleep attacks can occur against a background of normal alertness.