A 16-month-old male neutered cat was referred due to a history of right hindlimb lameness over several days. Radiography by the referring veterinarian revealed an osteolytic lesion at the right ilial wing. Haematology and blood chemistry were unremarkable besides borderline values of alkaline phosphatase (74 U/L). For further workup, thoracic, abdominal and pelvic computed tomography (CT) were performed. CT confirmed the presence of an osteolytic mass with additional osteoneogenesis in the right ilial wing and indicated no evidence of metastatic disease. Resection of the mass was carried out using partial iliectomy with preservation of the limb. Histopathology confirmed the mass as osteosarcoma. Follow-up was accomplished by radiographic re-check of the ilium every few months. On the 1-year follow-up, the cat was clinically healthy with no signs of lameness. Follow-up radiographies of the pelvis up until the time of writing this report showed no signs of tumour recurrence. DIFFERENTIAL DIAGNOSISDifferential diagnoses included benign bone lesions such as bone cysts as well as malignant bone tumours (osteosarcoma,