Osteochondrosis of the shoulder joint in the horse was diagnosed radiographically in 54 shoulders of 38 horses. Clinical signs were those of an intermittent lameness characterized as a swinging leg shoulder lameness with pain elicited by extension, flexion or abduction of the limb. Diagnosis of shoulder lameness was supported by blocking the shoulder joint with local anesthetics. Radiographic changes consisted of: (1) alteration in the contour of the humeral head and glenoid cavity, (2) periarticular osteophyte formation, (3) sclerosis of the subchondral bone, and (4) bone cyst formation. The primary bony lesion in the shoulder of the horse is similar to that described in the dog, pig, bull, turkey and broiler chicken. Secondary joint disease is a prominent finding with osteochondrosis of the shoulder in the horse. A follow-up study of 17 horses indicated that many of the affected horses had been sold and were being used for pleasure riding and breeding purposes. Those horses still in use usually had less severe radiographic changes at the time of diagnosis.