Many patients with assumed idiopathic REM sleep behavior disorder (RBD) may actually represent an early clinical manifestation of an evolving neurodegenerative disorder, such as the alpha-synucleinopathies, Parkinson's disease or multiple system atrophy. Early detection of these patients is clinically relevant for long-term prospective as well as future neuroprotective studies. For this purpose, we validated a 10-item patient self-rating questionnaire (maximum total score 13 points) covering the clinical features of RBD. The RBD screening questionnaire (RBDSQ) was applied to 54 patients with polysomnographically confirmed RBD (29 men; mean age 53.7 +/- 15.8 years), 160 control subjects (81 men; mean age 50.8 +/- 15.5 years) in whom RBD was excluded by history and polysomnography (PSG, control group 1) and 133 unselected healthy subjects (58 men; mean age 46.9 +/- 12.3 years; no PSG, control group 2). In most subjects (n = 153) of control group 1, other sleep-wake disturbances were present. The mean RBDSQ score in the RBD group was 9.5 +/- 2.8 points compared with 4.6 +/- 3.0 points in control group 1 (P < 0.0001). Considering an RBDSQ score of five points as a positive test result, we found a sensitivity of 0.96 and a specificity of 0.56. The RBDSQ poorly discriminated patients with the most challenging differential diagnoses such as sleepwalking or epilepsy. In control group 2, the mean RBDSQ score (2.02 +/- 1.78) was significantly lower than in the RBD group (P < 0.0005), revealing a specificity of 0.92. Due to its high sensitivity, the RBDSQ appears to be particularly useful as a screening tool.