We evaluated the validity, reliability, and potential responsiveness of the Beck Depression Inventory (BDI) in patients with Parkinson's disease (PD). In part 1 of the study, 92 patients with PD underwent a structured clinical interview for DSM major depression and based on this patients were considered depressed (PD-D) or nondepressed (PD-ND). Subsequently, patients filled in the BDI. In part 2, a postal survey consisting the BDI was performed in 185 PD patients and 112 controls. Test-retest reliability was assessed in 60 PD patients. The factor analysis revealed a cognitive-affective and a somatic factor. Cronbachs β£ for the BDI was 0.88. Mean BDI indicated significant differences (P Ο½ 0.001) between the PD and control group, between the PD-ND and PD-D group, and between PD-ND and control group. In part 1, the receiver operating characteristic curves showed that the area under the curve for the total BDI was 0.88. A cutoff was calculated for the BDI (14/15) that had the highest sum of sensitivity (0.71) and specificity (0.90). In part 2, the test-retest reliability for the BDI total score was 0.89 (intraclass correlation coefficient). The smallest real difference was 3.3 for the total BDI. The BDI is a valid, reliable, and potential responsive instrument to assess the severity of depression in PD. However, an adjusted cutoff is recommended.