OBJECTIVE: Patients with Parkinson's Disease(PD) have diminished health related quality of life (HRQoL) due to a number of emotional, functional and physical limitations. We examined the reliability and validity of the PDQ-39 as both a discriminant and evaluative instrument for use in Parkinson's disease studies. METHODS: We conducted a literature review using MEDLINE and HealthStar citing the PDQ-39, from 1995-2005 using the terms “Parkinson's Disease Questionnaire or PDQ-39” limited to Humans and English language. We reviewed each publication for evidence supporting the instrument's reliability face and content validity, construct validity measured as the correlation of the PDQ-39 responses with other relevant instruments and clinical measures, and test-retest reliability or intra class correlation coefficients. Discriminant abilities were evaluated by looking for evidence of significance between PD patients with varying levels of disability. Responsiveness was evaluated using change scores and established minimally important difference(MID). RESULTS: Thirty-nine papers met the inclusion criteria. Correlation of scales of the PDQ-39 with the Medical Outcomes Study 36-item Short Form (SF-36) showed strong correlation (>0.5). Intraclass correlation coefficients for each domain of the PDQ-39 ranged from 0.67 to 0.96 across studies. Mean scores for each domain were shown to be significantly statistically different (p<0.01) between PD patients with Hoehn & Yahr rating I, II, III, and IV. Changes in PDQ-39 scores were significantly correlated with changes in patients' retrospective judgments of change (0.25-0.31,p<0.01), and changes on the SF-36 (0.25-0.37,p<0.05), but not with clinical assessments. Two studies calculated a MID for the PDQ-39 which varied between 5 – 10 points on the summary index and 2-11 points across domains. CONCLUSION: There is substantial evidence supporting the reliability and validity of the PDQ-39 as a discriminate instrument, but further research on its usefulness as an evaluative instrument is warranted to increase our confidence.