Participants will be 300 patients with a confirmed clinical diagnosis of knee OA who receive their medical care in a large health maintenance organization (HMO) in Indianapolis, Indiana. We will randomly allocate geographically discrete offices of the HMOs to experimental (OA care by algorithm) or control (routine OA care) conditions (150 subjects/group). Patients who enroll in the study at each location will receive care for knee OA for 1 year under the guidelines specified by random assignment.