To determine the frequency of severe hypoglycaemia during conventional insulin therapy in juvenile-onset and adult-onset type 1 and in type 2 diabetes mellitus (DM), we retrospectively analysed the medical records of 165 Turkish diabetic patients who have been treated with conventional insulin. Patients were divided into 3 subgroups with respect to the type of diabetes: 33 had juvenile-onset Type 1 DM, 18 had adult-onset type 1 DM, and 114 had type 2 DM. The diabetic subgroups were found to be comparable with regard to mean frequency of severe hypoglycaemia (juvenile-onset type 1 DM: 0.20 episode x patient(-1) x year-1, adult-onset type 1 DM: 0.10 episode x patient(-1) x year(-1), type 2 DM: 0.15 episode x patient(-1) x year(-1)). Frequency of severe hypoglycaemia necessitating in-hospital treatment was 0.05 episode x patient(-1) x year(-1) for all diabetic subgroups. The data clearly indicate that the extent of the problem of severe hypoglycaemia during conventional insulin therapy in type 2 DM is comparable with both juvenile and adult-onset forms of type 1 DM in Turkish diabetic population.