We present the case of a 22-year-old woman with an aneurysmal cyst of the right proximal radius, treated by resection and a free bone graft (microvascular fibular transfer), without recurrence after 4 years. Over a 4 month period, there was a rapidly expanding and lytic lesion found in the radius. There were symptoms of elbow and wrist pain and early radially innervated muscle weakness. Radiological examination showed a localized tumour of the proximal radius, type 2, grade C, according to the classification of Campanacci. Biopsy led to the diagnosis of an aneurysmal bone cyst. Complete tumour resection was followed by a free vascularized fibular bone graft, resulting in good functional improvement, without local recurrence. Aneurysmal bone cysts are a rare condition, and the location in the radius has not previously been described. Vascularized bone grafts are mechanically and biologically superior in this type of case.