BACKGROUND The advantages of intramedullary fixation of pertrochanteric hip fractures over dynamic screw-plate devices in the clinical setting are still a matter of debate. We performed a case series study in a teaching hospital to analyse the results of the recent AO-ASIF proximal femoral nail (PFN). METHODS Between July 1998 and May 2001, 46 consecutive patients (47 fractures) were included in the investigation. The average patient age was 76.4 years (range 50-93 years), and most fractures (74.5%) were unstable. Operative details, adequacy of fracture reduction, screw position in the femoral head, re-operations, and postoperative complications were documented. Functional results were evaluated by the Parker and Palmer mobility score and Barthel Index for patients with a minimum follow-up of 4 months. RESULTS Intraoperative technical or mechanical complications occurred in 11 patients (23.4%), mostly problems with the distal nail locking and fracture of the lateral wall of the greater trochanter. Mean surgical time was 83.4 min. The lateral protrusion of screws causing thigh pain was the most common postoperative complication, with an incidence of 21.2%. There was only one femoral shaft fracture at the nail tip caused by a fall at 9 months of follow-up. Five patients (10.6%) had intra-articular migration of screws, which was associated with loss of reduction and varus collapse in one case. There were 2 persistent deep infections and 2 haematomas that required surgical drainage. The re-operation rate was 19.1%, mainly cephalic screw removal due to lateral protrusion at the proximal thigh. Ten patients (32.2%) fully recovered their Parker and Palmer mobility score, and 20 patients (66.6%) recovered more than 90% of their pre-injury Barthel Index values. The average limb shortening was 14 mm. Mortality rate during the observation period was 20.4%. CONCLUSIONS In view of only one loss of reduction with varus collapse clearly caused by a technical error, we concluded that the PFN is a suitable implant for unstable fractures, but the high re-operation rate precludes its routine use for every pertrochanteric fracture.