Osteochondritis dissecans (OCD) is a joint disease characterized by focal separation of the articular cartilage and subchondral bone, which can cause flap or free cartilage fragment detachment. Osteochondritis dissecans of the proximal humerus is a frequent cause of foreleg lameness in young large breed dogs, and some breeds are predisposed. Clinical signs in dogs are bilateral anterior leg lameness, which occurs mostly at the age of 4-9 months. Conservative or operative treatment may be preferred, depending on the patient's age, clinical symptoms, and the extent of the lesion. In this presentation, clinical and radiological examination findings, diagnosis and treatment of OCD on the caudocentromedial surface of the humeral head in the dog are described. In the detailed anamnesis of an 8-month-old, 22 kg, Border Collie male dog brought to the Surgery Clinic of Istanbul University-Cerrahpaşa Faculty of Veterinary Medicine with the complaint of left foreleg lameness, it was learned that there was pain exacerbated by exercise, NSAI was applied, exercise was restricted, but clinical symptoms did not improve. Physical examination revealed significant pain in flexion and extension of the scapulohumeral joint, and mild atrophy of the m.supraspinatus, m.infraspinatus and m.deltoideus . Radiographic examination revealed an irregular concave image with a rounded lucent area along the caudal humeral head associated with mild subchondral sclerosis in the mediolateral position of the left scapulohumeral joint. CT scan performed for definitive diagnosis showed subchondral bone sclerosis and large, irregular subchondral bone defect on the left humeral head. OCD flap in the left shoulder joint and necrotic tissues in the region were removed by arthrotomy. Exercise restriction was recommended to the patient for four weeks. It was observed that the patient started to use the left front extremity intermittently in first week post-operatively, and used it with mild lameness in about 15-25 days. In conclusion, in this case, it was seen that CT provides more specific images than direct radiography for the diagnosis of OCD, and the prognosis is good with appropriate treatment and postoperative care.