Legg-Calvé-Perthes disease rarely develops during adolescence. However, when it does, its long-term course is always disabling. Thirteen patients whose age at diagnosis ranged from 13 to 15 years were followed up from a minimum of 7 years to a maximum of 42 years (average follow-up 27.6 years). At diagnosis, eight hips were Catterall group II, five group III, and one group IV. All the patients developed pain and restriction of motion of the affected hip between the end of treatment and 39 years of age, and two of them underwent radical surgical procedures. At follow-up, 10 hips that were radiographed showed signs of osteoarthritis.