A survey of cadaver material was undertaken in order to determine the prevalence of arthritis of the canine stifle joint. One hundred and fifty unselected cadavers were obtained from veterinary practices for this purpose, and their stifle joints were radiographed and dissected to discover abnormalities. Thirty-one dogs (20 per cent) had stifle arthritis and in all except one the lesions were characteristic of osteoarthritis. In the exceptional case infection was the cause. A mechanical derangement was present in 20 of the 54 affected joints, in the form of rupture of the anterior cruciate ligament (10), meniscal tears (9) and patellar dislocation (1). The cause of the arthritis in the other 33 joints is unknown.