A 49-year-old man had posttraumatic persistent calf swelling and a tibial and fibular fracture. Despite the intramedullary nailing of the fracture, the swelling did not improve, and at the 6th postoperative week it was misdiagnosed (using venogram) as deep vein thrombosis. Therefore, it was mistreated with anticoagulants, which led to great deterioration of the local signs. An arteriogram revealed an initially missed false peroneal artery aneurysm. Surgical treatment was performed immediately. The 6-week delay had led to some atrophy of the posterior compartment muscles, fortunately without any permanent disability. The importance of proper and early diagnosis of posttraumatic persistent calf swelling is stressed.