Aneurysmal bone cysts account for less than 1% of primary bone tumours and have a predilection for the metaphyses of the long bones of the leg. Only 1% of all aneurysmal bone cysts occur in the patella. We report on a 30-year-old man with a primary aneurysmal bone cyst in the right patella treated with curettage. The defect was filled with demineralised bone matrix and allogeneic cancellous bone graft. At the 1.5-year follow-up, the bone graft was well incorporated, the patient experienced no pain or tenderness and had a full range of knee movement.