Four horses (two mares and two stallions) with severe tarsal swellings were admitted to the surgery clinic at Faculty of Veterinary Medicine, Cairo University. Full case history and thorough clinical, radiographic, ultrasonographic and arthroscopic examinations were carried out on all the horses. The age of the affected animals ranged from 3-8 years. Osteochondrosis dissecans (OCD) was either unilateral or bilateral. Two animals had 0/5 degree of lameness and 2 had 2/5 degree of lameness. Two animals had bog spavin and two had bone spavin. Radiographic findings included osteochondral fragment with flattened or irregular contour of the subchondral bone surface at the intermediate ridge of tibia (2 cases), the medial malleolus of tibia (one case) or at the medial trochlear ridge of talus (one case).  Ultrasonographic findings included joint effusion with anechoic fluid (synovitis), presence of echoic fragment inside the synovial fluid with acoustic shadowing and area of thickened cartilage. Arthroscopically, osteochondrosis dissecans fragments were clearly seen with congestion and bleeding in the articular surface. All horses responded well to the arthroscopic removal of the osteochondral fragments and returned to work two months post-surgery.