Imaging studies are performed on patients with arthritis for a variety of reasons: to determine whether an arthritic condition is present; to establish the specific diagnosis; to determine the extent of disease; to assess the activity of disease; to detect complications of disease; to evaluate progression of disease; to judge the efficacy of drug treatment; to help in selection of surgical candidates; to aid in the choice of surgical procedures; to size, design, or fabricate prostheses; and to identify complications of surgery. Conventional radiography is still the mainstay of all examinations in arthritic patients. Arthrography is best applied to evaluate complications of disease and of surgery, although it may be useful in disease detection and in determining the specific diagnosis. Nuclear medicine studies are best used to identify complications of surgery and may also be useful to assess disease activity or extent. Ultrasound is useful to detect dissecting synovial cysts and deep venous thrombosis. The most valuable role of computed tomography is in the design and fabrication of prostheses and in evaluating complex anatomy of involved joints. Magnetic resonance imaging may be useful in early detection of articular cartilage damage and may assist in determination of the specific diagnosis; enhancement with contrast material may aid in assessment of disease activity.