A Statewide register of insulin-treated diabetic patients has been established in Tasmania. The register is the first of its kind in Australasia. Insulin treatment was chosen as the criterion for admission to the register because it was a suitably "hard" end-point, and because the completeness of the register could be validated easily by insulin prescription statistics. Both subjects with insulin-dependent diabetes mellitus and those with non-insulin-dependent diabetes mellitus (who happened to be treated with insulin as of the prevalence date, May l, 1984) are eligible for registration in the prevalent population. Furthermore, no age restrictions have been placed upon entry. It is to be hoped that this all-inclusive policy will assist in the development of an epidemiological definition of insulin-dependent diabetes mellitus. Access to cases has been by hospital records, general practitioners, lay bodies and general publicity. Of over 600 diabetic subjects who were contacted during the first 12 months of the study (approximately one-half of the estimated prevalent population), only three declined to join the register. Once fully established and validated, the register will be used to test aetiological hypotheses in addition to providing descriptive cross-sectional information about diabetes in Tasmania. It is intended that a longitudinal study of insulin-treated diabetes will follow once the cross-sectional information is complete.