We studied 10 patients treated because of late avascular necrosis (AVN) mimicking Legg-CalvéPerthes' disease (LCPD) after developmental dislocation of the hip (DDH). DDH was recognized late at an average age of 5.4 months and in all children it was treated without surgery. In 4 children, the treatment was complicated by mild AVN of the femoral head, which had disappeared before 3 years of age. The first clinical signs of LCPD were noted at a mean age of 5.8 years. They all had Catterall's type III or IV of LCPD. The course was typical of LCPD. 8 children were operated on at mean age of 7.4 (5-12) years. In 7 of them, subtrochanteric derotation-varisation osteotomy of the femur with shortening combined mainly with Dega's pelvic osteotomy was done. The operative treatment resulted in a concentric position of the femoral head and good coverage of the acetabulum. Follow-ups were done at 10 (6-35) years. Shortened femoral neck and trochanteric overgrowth occurred in 4 operated hips. According to the Stulberg classification, 2 hips were classified as type I, 1 as I/II, 5 as II, 1 as II/III and 1 as IV. We conclude that LCPD mimicking late AVN can occur in hips treated because of developmental dislocation.