One hundred nineteen loosenings of Müller total hip endoprostheses are analyzed. These arise from 1,407 operations performed between 1969 and October 1977. Deep infections occurred in 7 cases (0.5%). Loosening after a minimum of 5 years occurred in 15.3%. Of these the stem only was involved in 73.7%, stem and socket in 11.8% and the socket only in 14.5%. Seventy-eight per cent of the loose femoral components had been implanted in a varus position, with a long neck showing a higher incidence of failure, along with cases of implantation for osteoarthritis with cystic changes of the femoral head. In six cases the femoral component broke. This occurred twice in the acetabular component. Pain and loosening seemed to occur at the same time, and was unusual more than 5 years after the operation. When loosening occurred later, it was frequently caused by a fall.