Giant cell tumor (GCT) is a tumor found most often in the ends of long bones and is essentially located in the epiphyseal or metaphyseal or epiphyseal equivalent portions of bone. It is a locally aggressive neoplasm, generally arising in adults between the ages of 20 and 40 years, clinically possessing metastatic potential. The classic location is around the knee joint and it starts in the epiphysis spreading to the metaphysis and may erode the cortex in 25% of the cases. Approximately 10% of these tumors have a malignant course. The patella is a rare site with a reported incidence of less than one percent. Rare multicentric forms have been reported. A 14-year-old female from Malang, East Java, presented with a one year history of a progressively growing mass in the left patella associated with slight pain that has been aggravated with activity for 6 months. Plain X-ray left knee AP and lateral views reveal expensile lytic lesion in left patella with marked thinning of cortex in anteroinferior aspect with few sclerotic septa within. MRI of left knee shows approximately 3x2x2 cm heterogeneous lobulated expensile soft tissue mass in left patella extending up to the articular surfacewithfluidfluidappearance. No evidence of extension into the joint space. From fine needle aspiration cytology, resulting giantcell tumor with deferential diagnosis of aneurysmal bone cyst. Operation was already performed. Curettage, bone graft and biopsy were taken. Immunocytochemical smear was performed and confirmed as giant-cell tumor of the patella. At present, 6 months after the operation, the patient has no arthralgia and full range of motion for the knee.