We studied the morphology of the contralateral femur in 10 patients with subcapital fractures, 10 with trochanteric fractures and 10 with unilateral osteoarthritis. We found that the patients with trochanteric fractures had a significantly shorter femoral neck (4.5 +/- 0.5 cm) than patients with subcapital fractures or osteoarthritis (5.4 +/- 0.4 cm). It may be that this difference in femoral neck length is related to the site at which a proximal femoral fracture occurs.