The rate of post-operative dislocation after primary total hip arthroplasty in 1739 cases was 3.3 per cent; 0.9 per cent being classified as recurrent dislocations. Malposition of the socket, limb shortening or any other single technical factors could not be demonstrated to be responsible for post-operative dislocation of the hip. A previous osteotomy predisposed for dislocation, but in no case was this dislocation classified as recurrent. Cases with a previous cervical-femoral fracture were significantly more commonly dislocated compared with coxarthrosis cases. This fact probably could be explained by a high rate of alcoholism in men and old age in women.