A 75-year-old male patient was referred to our orthopaedic department due to progressive weakening of the left leg, noticed while going up and down stairs, and swelling of the thigh. An increase in swelling was noted in association with spicy food. Clinical examination showed a palm-sized non-pulsatile soft mass in the popliteal region and swelling in the posterior-lateral thigh. MRI revealed a space-occupying 40×15×10 cm mass extending into the upper thigh without infiltrating character. Angiography was negative. Open surgical biopsy was performed to rule out a soft tissue tumour, during which, connection to the popliteal artery was identified. The patient underwent excision of the aneurismal sac and a prosthetic graft was interplaced. On follow-up, the patient noticed a rapid increase in muscle strength; stairs were no longer a problem.