The purpose of this study was to evaluate prognostic risk factors related to a poor radiological outcome. The study consisted of 74 patients with Legg-Calvé-Perthes disease treated using a Thomas splint. The modified Herring lateral pillar classification and the reviewed Stulberg classification system were applied. A significant correlation between the Herring group and Stulberg was found (P=0.03). There was a significant correlation between age at onset of the disease and Stulberg outcome (P=0.05). The Herring classification correlated to the Stulberg outcome. An age of 7 years or more at onset was considered as a risk factor for a poor Stulberg outcome.