The Hospital Anxiety and Depression Scale (HADS) has been used in Parkinson's disease (PD) but information about its psychometric properties in this context is limited. The aim of this study is to assess the psychometric properties of the HADS in PD. In an observational, cross-sectional analysis, HADS data quality, acceptability, scaling assumptions, internal consistency, construct validity, and precision were explored. From a sample of 387 PD patients, 22% and 14% scored > or =11 points (definite case) on the HADS anxiety and depression subscales, respectively. Cronbach's alpha was 0.81 and 0.83 for these subscales. Factor analysis revealed two factors (49.8% of the variance) representing anxiety and depression. The HADS closely correlated with health-related quality of life (HRQL) measures and displayed satisfactory discriminative validity for patients grouped by severity level, disease duration, HRQL status, and treatment. The SEM was 1.84 for HADS-Anxiety and 1.72 for HADS-Depression. The HADS is an acceptable, consistent, valid, precise, and potentially responsive scale for use in PD.