Failed placement of the prosthesis stem causes patterns of stress which are reflected in atypical bone absorption and may result in premature loosening. 64 patients, who underwent implantation of ABG I- or Zweymüller SL-hip endoprostheses between 1990 and 1994 in the Clinic for Orthopaedic and Physical Medicine at Martin-Luther-University Halle - Wittenberg, were examined within a prospective study on a voluntary basis. Bone mineral density was measured, radiographic and clinical aspects were evaluated. The average period of time for postoperative analysis was 96 (ABG) or 104 (ZM) months. Especially focusing on the position of the prosthesis, clinical (Merle d' Aubigné-Score), densitometric (DEXA) and radiographic analyses were carried out. 27,5 % of the ABG- and 37,5 % of the ZM-endoprostheses have been implanted in varus position. 15 % of the ABG- and 8,3 % of the ZM-prostheses have been implanted in valgus position. The majority in both groups of patients showed good or excellent clinical results irrespective of the position of the prostheses. Differences in the localisation of radiographic phenomena depending on varying positions of the prosthesis were apparent due to altered patterns of stress, but were not significant. Variation from the neutral position lead as well to pathologic periprosthetic patterns of bone density. A precisely fixed prosthesis is the precondition for achieving good long term results. Furthermore, it reduces the risk of premature loosening. Therefore, the position of the prosthesis should be monitored with the help of intraoperative X-ray analysis.