The World Health Organization Disability Assessment Schedule (WHO DAS II) is a new measure of disability based on the ICIDH-2 model of functioning and disability. This study evaluates the measurement properties of the WHO DAS II in two disorders commonly encountered in the primary care setting. Seventy-three patients with depression and 76 patients with back pain were interviewed at baseline and after 3 months of usual primary care. Internal validity, convergent validity, and responsiveness to change of the WHO DAS II were evaluated. The WHO DAS II had excellent internal validity and convergent validity in the primary care setting. The responsiveness to change of the WHO DAS II was comparable to that of the SF-36. The WHO DAS II appears to be a useful health status instrument for measuring the disability associated with both physical and mental disorders in the primary care setting. This instrument facilitates the use of the ICIDH-2 as a framework for evaluating activity limitations and participation.