We reviewed the polysomnograms (PSGs) of 292 consecutive patients with sleep disorders (Parkinson's disease (PD), n=19, other sleep disorders, n=273) to investigate the sensitivity and specificity of the clinical diagnosis of rapid eye movement behavior disorder (RBD) compared with polysomnographic diagnosis. Patients with dementia, multiple system atrophy, or any other neurodegenerative disease were excluded. RBD was diagnosed clinically if the minimal criteria, according to the guidelines given in the International Sleep Disorders Classification, were fulfilled. The following PSG criteria were required for diagnosis of RBD: REM sleep without muscle atonia seen in PSG associated with motor behavior visible in the PSG-synchronized videotape. Nine of nineteen PD patients (47%) had RBD. RBD occurred in only four patients without PD (1.8%). The sensitivity of specialized interviews for identifying RBD clinically was good in non-PD patients (sensitivity: 100%, specificity: 99.6%). However, the sensitivity was poor (33%) with a specificity of 90%, in patients with PD. We conclude that the diagnosis of RBD in patients with PD requires PSG, whereas interviews are sufficient for diagnosing RBD in non-PD patients.