Introduction: Aneurysmal bone cysts constitute less than 1% of primary bone tumours in humans and are usually present in the region of the metaphysis of the long bones of the leg. Less than 1% of all aneurysmal cysts involves patella. We are reporting a case of primary aneurysmal bone cyst in the right patella in a 27-year-old man treated with excisional curettage and bone grafting with cementing. At the 1 year follow-up, the patient was pain-free with a full range of motion of the knee joint. Aim: Primary aneurysmal bone cyst of the patella. Result: The clinical examination and history did not suggest any recent trauma or signs of inflammation. Tenderness was present in the patella and there was knee swelling as compared to the contralateral side. Conclusion: Local examination revealed tenderness in the patella and irregular, supra-patellar, infra-patellar and para-patellar fullness in the anterior aspect of the knee, with a full range of motion of the join.