A retrospective study of 118 femoral neck fractures treated with multiple Knowles pins or with AO (ASIF) cancellous bone screws, and followed for at least 22 months, revealed nonunion in 1/33 undisplaced fractures and in 27/85 displaced fractures. Avascular necrosis was radiographically evident in respectively 2/32 and 19/58 united undisplaced and displaced fractures. Four factors were adversely associated with union: inaccurate reduction, mental confusion, age above 80 years and fixation with less than 6 Knowles pins. Late segmental collapse was not significantly related with any of the 9 analyzed factors. It was concluded that displaced femoral neck fractures in confused patients older than 80 years, or fractures one cannot adequately reduce, should be primarily treated with arthroplasty. Following accurate reduction, internal fixation with less than 6 Knowles pins cannot be recommended.