Objective: To asses the epiphyseal development of the unaffected hip in unilateral perthes disease. Patients and methods; Thirty two patients with unilateral perthes disease,their normal unaffected hip joints compared with forty normal children regarding their ossification of the proximal capital femoral epiphysis over aperiod of two years . Results; The epiphyseal height of the normal hip in unilateral Perthes disease was less than for the normal children (compared group).Conclusion;Delay in ossification of the proximal head may be one of the risk factors for Perthes disease.