To study the bone age delay patterns in different stages of Perthes disease, 140 hand and corresponding hip radiographs in 83 patients were assessed. In the hand radiographs, the radius, ulna, metacarpals and phalanges (RUS) and carpal bone ages were calculated using the Tanner and Whitehouse 3 method and the Greulich and Pyle (G and P) bone age was assessed using the G and P atlas. From corresponding hip radiographs, the modified Elizabethtown stage was assessed. The RUS and carpal bone age as well as G and P bone age were found to lag behind the chronological age. The 95% confidence interval for the difference between RUS and G and P bone ages was 0.19 to 0.43 years and between carpal and G and P bone ages was -0.516 to -0.14 years, indicating a close agreement between the Tanner and Whitehouse 3 and G and P methods. The RUS bone age delay was maximum in stage Ia (2.00 +/- 1.08 years), whereas carpal delay was maximum in stage IIa (2.15 +/- 1.28 years). Bone maturation acceleration was observed in later stages of the disease as bone age tried to catch up with chronological age. Carpal delay was significantly greater than RUS delay from stage Ib to IIIb (P<0.05), but no significant difference was observed between carpal and RUS delays in stage IV (P=0.21), implying that bone maturation acceleration occurs in the RUS in the earlier stages, and carpal bone age tends to catch up with RUS bone age in the healed stage of the disease. The RUS and carpal bone age delays in stage I were significantly greater in severe (Catterall groups 3 and 4) disease than in mild (Catterall groups 1 and 2) disease. All patients in whom RUS or carpal bone age delay in stage I was greater than 2 years subsequently developed severe disease, indicating a positive correlation between bone age delay in stage I and subsequent extent of involvement of capital femoral epiphysis.