In order to obtain new and more detailed information about temporal trends and geographic distribution of Type 1 (insulin-dependent) diabetes mellitus in Sardinia, we screened a series of birth cohorts (1936-1973) of all male army conscripts aged 18-19 years, filed in the Sardinian Conscript Register where Type 1 diabetes is a cause of rejection. A total of 678 diabetic subjects, born and permanently residing in Sardinia, was identified. The point prevalence (x 1000) at the age of 20 years in the birth cohorts ranged from values close to zero for the first ten cohorts (1936-1945) up to a maximum of 3.08 (95% confidence limits 2.28-4.08) for the 1966 cohort and continued high thereafter although an apparent decrease was observed from the early 1970s birth cohorts. Type 1 diabetes was distributed throughout the four provinces of Sardinia with no particularly significant heterogeneity; however, in accordance with the geographical distribution of diabetes cases of the Eurodiab Ace survey (1989-1990), the highest prevalence of the disease was observed in the Cagliari and Oristano provinces, followed by Nuoro and Sassari. These data suggest a gradually increasing trend of male Type 1 diabetes prevalence in Sardinia with a 29-fold increase between the late 1930s and the late 1960s birth cohorts. This seems to confirm the high incidence of Type 1 diabetes in the 0-14 and 0-29 year age groups recently reported among Sardinians during the Eurodiab Ace collaborative multicentre study.