Hypertrophic osteodystrophy was diagnosed in 16 male and 2 female puppies aged between 2.5 and 8 months. All animals had stiff and stilted gait, painful swellings in the metaphyseal areas of the antebrachium and tibia, pyrexia, weakness and diarrhoea as common symptoms. Radiological examination of the affected areas showed extraperiosteal bone proliferations. With chronicity, the new bone formation spanned the entire diaphysis from the distal to the proximal metaphysis. Two dogs were treated with parenteral administration of analgesics, corticosteroids, vitamin C, and antibiotics in addition to dietary management. These 2 puppies, which had shown a clinical improvement during the long therapy period, died immediately after the cessation of drug administration. Fifteen animals recovered completely. These 15 puppies underwent dietary management only. The other dog was euthanised without any treatment at the owner's request. In the histopathologic examination of 2 dogs, in which a necropsy was performed, epiphyseal plates were structurally normal. However, primary and secondary spongiosa immediately below were observed to have been destroyed, extending up to the metaphyseal zone, and resorption had occurred in some areas. In the periostal zone, extraperiostal ossification, foci of bone destruction due to the osteoclastic activity, development of fibrous tissue, and infiltration by numerous neutrophils were observed.