The incidence and prevalence of insulin-dependent diabetes mellitus (IDDM) and impaired glucose tolerance (IGT) were studied in a series of 273 patients with thalassaemia major followed in Ferrara from 1954 to 1998. It was found that the prevalence of glucose metabolism abnormalities has decreased and that the mean age of diagnosis has increased over the years. Risk factors associated with IDDM and IGT were lack of compliance with chelation therapy, iron overload and the presence of cirrhosis and severe fibrosis.