Fragmented coronoid process in 13 elbows (10 dogs) was treated by medial elbow arthrotomy plus osteotomy of the proximal ulnar diaphysis. All the dogs were skeletally immature and had a lameness of at least four weeks' duration. An attempt was made to measure the disease-modifying effect of this procedure by estimating the development of osteophytosis. Complications were infrequent and never serious. Clinical outcome, overall, was good. This preliminary work indicates that proximal ulnar diaphyseal osteotomy may have a place in the management of fragmented coronoid process in young dogs.