The Quebec Back Pain Disability Scale is a new measure of functional disability for patients with back pain. Functional disability was operationalized in terms of perceived difficulty associated with simple physical activities. The content of the scale was developed in several stages, including a literature review, two studies seeking the opinions of patients and experts, pilot testing, and a large, longitudinal study of back pain patients. Forty-eight disability items were extensively studied using standard methods such as test-retest reliability, item-total correlations, and factor analysis, as well as modern techniques based on item response theory. Items that were highly effective in discriminating between different levels of disability were selected for the final, reduced scale. The scale has 20 items, representing six empirically derived categories of activities affected by back pain. Measurement properties of this instrument have been previously discussed.