A total of 110 fractures of the neck of femur were studied in 108 patients 17 to 50 years old. The aims were to analyze why these fractures occur in young adults, and what results can be expected after internal fixation. Severe trauma caused about half of the fractures. In the remaining group chronic and disabling disorders were usually present at the time of injury. Seventeen patients were known to abuse alcohol. Aseptic necrosis with late segmental collapse occurred in 41 per cent of the hips (45/110), comparatively more often in patients who were 45 years or younger. Only 16 of the 73 patients who were seen at follow-up (22 per cent) had a perfect result. It is concluded that femoral neck fractures in patients younger than 45 years occur because of significant trauma in a healthy subject, or minor trauma in subject with predisposing disease. The incidence of late segmental collapse is greater than in elderly patients with femoral neck fractures. A less satisfactory result can therefore be expected.