Background. This article presents long-term outcomes in the surgical treatment of children in the early phase of Perthes' disease, i.e. Reinberg phases I and II. Material and methods. From among 650 children operated during the period 1976-1998, 128 patients reported for follow-up, including 102 boys and 26 girls, who had been operated by transverse inter- and sub-trochanteric osteotomy according to the authors' own concept. These children ranged in age at surgery from 3 to 13 years (average 7 years); the observation period ranged from 5 to 25 years (average 11 years). The radiological picture of the femoral head in long-term follow-up after surgery was assessed according to the Stulberg and Mose classification schemes. Results. There were 72% good outcomes, 23% satisfactory, and 5% poor. Retrospectively, 105 hips (81%) of the total 128 were classified radiologically to Herring group A or B. This large percentage of A and B results indicates that the disease process was just beginning, and had not yet involved the entire femoral head. Of all the operated patients, 77 (60%) did not go through the fragmentation period or only just entered the initial phases of stage III. Conclusions. Our observations would indicate that in the course of surgery the progress of the disease is halted, as though the femoral osteotomy released an unknown factor limiting the development of the disease and halting its progress at the phase at which the surgery is performed.