Age at onset of multiple sclerosis (MS) can vary from childhood to adult life. Many reports have been carried out over the years concerning the role of age at onset in determining the disease outcome. In a sporadic MS population of 1463 patients with homogeneous clinical and demographic features, derived from three Italian neurological centres (Bari, Cagliari and Sassari), we analysed the relative weights of current age and age at onset on disease severity according to the expanded disability status scale (EDSS) score, by fixing the disease duration. The results of present study demonstrate that clinical disability in MS is influenced by the patient's age (p < 0.01) and not by the age at onset. Therefore, these data do not confirm the hypothesis that an early age at onset should be considered a favourable prognostic factor of the disease outcome.