An aneurysmal bone cyst was diagnosed in the pelvis of a 3 1/2-year-old domestic short-hair cat. Clinically, the cat was suffering from tenesmus and dysuria. Radiographs showed an expansive lytic lesion appearing as a subperiosteal ‘blow-out’ of the ventral aspects of the pubic and ischial bones. Definitive diagnosis was provided by histopathology. The veterinary literature on aneurysmal bone cysts is reviewed.