This study evaluated the final outcome of coxa magna that developed as a sequela of Legg-Calve-Perthes disease. The final outcomes at skeletal maturity were assessed by the Stulberg classification in 85 children with unilateral Perthes disease. Among them, 21 children had a bilateral arthrogram at the active stage of the disease, and the arthrogram measurements were compared with those measured at disease healing and at skeletal maturity. Coxa magna was observed in 53% (45/85), with a mean increase in 20.0 +/- 7.2%. These coxa magna and resulting acetabular deformities occurred in the early stage of the disease. In 68 hips with mild (1-9% increase) or moderate (10-19%) coxa magna, the final results were Stulberg I or II in 57 hips and III in 11. In 17 hips with severe coxa magna (> or =20%), the results were I or II in one hip, III in nine, and IV in seven. This means that 41% of the hips with severe coxa magna might have osteoarthritis later in life.