Eighty-two infra-isthmal fractures of the femur were reviewed in order to develop a fracture classification, to determine the results of treatment, and to define the best treatment methods for certain specific fracture patterns. Type I (transverse or short oblique) fractures were seen in 36 patients (mean age, 33 years). They had a 25% complication rate when treated by open reduction, and a high malunion rate when treated by closed means. Type II (spiral or long oblique) fractures were generally caused by falls, and were seen in 36 patients (mean age, 56 years). Most patients treated by operation had an unsatisfactory result. Malunion was seen in 29% of the patients treated by closed means. The remaining ten patients had either severely comminuted (Type III), or pathological (Type IV) fractures.Intramedullary nail fixation should be used wherever possible in these fractures since many of the complications in the operative group were related to rigid plate fixation. Closed treatment resulted in an unacceptably high incidence of malunion in this study, particularly in Type I fractures. Conventional methods of internal fixation were not successful in dealing with Type II fracture, and alternative methods are proposed.