On the basis of 63 Salter pelvic osteotomies which were performed in 57 patients with congenital dislocation and subluxation of the hip between 1970 and 1986 at the Orthopaedic University Clinic of Vienna, we tried to work out the reasons for the rate of failures of 29% in our material. The mean age at operation was 4.1 years (1.5-18), that at follow up 15.7 years (4.6-28). We based our assessments on the clinical and radiological criteria of the Commission for the Study of Hip Dysplasia of the German Society of Orthopaedics and Traumatology. The number of failures at follow up (hip value III + IV) increased from 25%, if the operation was done before the age of four years, to 41%, if it was performed at a later age. In the latter group we were not able to observe any spontaneous improvement, which was typical for the younger age group. A moderately pathologic hip dysplasia (hip value III) could be improved to a normal value at follow up in 87%, an extremely pathologic one just in 50% of the cases. In just some of the patients we found postoperatively a tilt of the distal pelvic fragment, which could be registered by the oval shape of the foramen obturatum. Above all in young children a pelvic tilt was rare because of the elasticity of the triradiate cartilage. Out of 37 evaluable cases a tilt of the distal pelvic fragment by the operation could be verified in only 12 cases.(ABSTRACT TRUNCATED AT 250 WORDS)