BACKGROUND: The purpose of the study was to prospectively compare the functional outcome of intramedullary nailing of the femur performed with use of a trochanteric and a piriformis fossa entry portal. METHODS: One hundred and ten patients with a femoral shaft fracture were enrolled in a prospective, randomized study. Fifty-four patients were randomized to Group A (piriformis fossa portal) and fifty-six to Group B (trochanteric portal). Outcome measures included the Western Ontario and McMaster Universities (WOMAC) Osteoarthritis Index hip function score, pain, and blinded functional evaluation by a physical therapist. RESULTS: Most measures of hip function did not differ between the two groups. The WOMAC score at three, six, and twelve months did not differ significantly between the piriformis fossa and trochanteric nailing groups. Functional tests included the chair stand test and the timed up and go test. Patients in Group B had significantly better scores on the chair stand test (13.3 compared with 11.1 in Group A, p = 0.04) at six months postoperatively, but there was no difference at twelve months (14.0 compared with 13.6). The two groups did not differ significantly on the timed up and go test at either six or twelve months. The two groups also did not differ on the muscle strength testing. Intraoperative parameters differed significantly between the groups with respect to operative time, fluoroscopy time, and incision length, with the difference favoring Group B for each parameter. Analog pain scale values were similar in Group A (2.49) and Group B (2.15) at twelve months postoperatively. CONCLUSIONS: Patients in our prospective randomized study who were treated with trochanteric nailing did not differ in hip function at one year postoperatively compared with patients treated with intramedullary nailing through the piriformis fossa. The values of several intraoperative parameters were significantly better in the trochanteric nailing group. Our data indicate that the functional hip outcome of femoral intramedullary nailing performed through the greater trochanter is equal to that of intramedullary nailing performed through the piriformis fossa.