Two cases of Sudeck's atrophy of the foot occurring 16 months and 17 years after infected fractures of the leg were studied radiologically and pathologically. Various cartilaginous changes were observed, the nature and severity of which depended on the joint involved. They included superficial pannus, deep erosion, fibrous ankylosis and, at times, bony ankylosis. These changes are similar to those observed in nine cases studied by Rutishauser et al. Comparison of the pathological changes in human and experimental joint immobilization suggests that these changes are due mainly to decreased mobility of the joints of the foot in Sudeck's atrophy. These observations also suggest that physiotherapeutic mobilization in Sudeck's atrophy is important for the joints as well as for bone. From a more general point of view, they demonstrate that a condition which is nosologically different from the chronic rheumatic diseases can nevertheless cause lesions that are a fundamental part of the pathological changes in osteoarthritis, rheumatoid arthritis and ankylosing spondylitis.