A prospective, randomized trial of 104 consecutive patients with displaced fractures of the femoral neck treated with either a sliding screw plate or four AO cancellous bone screws was performed to study the influence of the fixation device and the fixation procedure on the vascularity of the femoral head. The vitality of the femoral head was determined by 99mTc-MDP scintigraphy performed 2-3 months after the operation. Eighty-seven patients (84 per cent) were available for assessment. The two treatment groups were comparable with regard to age, degree of primary displacement and quality of reduction. There were significantly more (P less than 0.01) avascular femoral heads or femoral heads with reduced vascularity in the sliding screw plate group (14/40, 35 per cent) than in the four AO cancellous bone screw group (5/47, 11 per cent).