Abstract.The patella is an unusual location for primary and metastatic bone tumors to develop. The most frequently encountered primary osteolytic lesions at the patella include giant cell tumors of the bone (GCT), chondroblastoma and aneurysmal bone cysts (ABC). However, the presentation of an ABC originating secondary to a GCT at the patella is rare. The present study describes such a case in a 46-year-old female. The differential diagnosis of the condition was extensive. The patient underwent curettage and the addition of bone cement to fill the defect. Pathological analysis of the resected tissue demonstrated that the lesion was consistent with an ABC forming secondary to a GCT. A 3-month follow-up was completed subsequent to the surgery, with a computed tomography scan demonstrating no evidence of recurrence. However, frequent and continuous observations of the patient following diagnosis are planned in order to evaluate the long-term efficacy of the surgical treatment. To the best of our knowledge, the present study describes the third reported case in the literature of this rare, double synchronous, benign tumor located at the patella.