The WOMAC (Western Ontario and McMaster Universities) Osteoarthritis Index is a tested questionnaire to assess symptoms and physical functional disability. We adapted the WOMAC for the German language and tested its metric properties, test-retest reliability and validity in 51 patients with knee and hip OA. All WOMAC scales (pain, stiffness, function) were internally consistent with Cronbach's coefficient alpha ranging from 0.80 to 0.96. Test-retest reliability was satisfactory with intraclass correlation coefficients ranging from 0.55 to 0.74. All scales and the global index calculated as the mean of scale scores had a bimodal distribution and a slight ceiling effect. As hypothesized the WOMAC scales were associated with radiological OA-severity and limitations of range-of-motion. Patients with more severe symptoms and functional disability perceived more limitations in their roles at home and at work. The presented German version of the WOMAC is a reliable and valid instrument for the assessment of symptoms and physical functional disability in patients with knee and hip OA.