The incidence rates of IDDM in Italy show remarkable variability. Sardinia, a region with the second highest incidence rate in the world, co-exists with other regions with lower rates. We review and compare epidemiologic data on the incidence of childhood-onset IDDM in Italy. papers published from 1980 to 1996 reporting incidence data in Italian areas were found by search of Medline and non-indexed Italian journals. The incidence data found cover only 57% of the Italian population. The analysis of our results shows how difficult it is to make a careful study of epidemiology of IDDM in Italy. The RIDI (the Registry for Insulin-dependent Diabetes mellitus in Italy) project started in 1996 according to international guidelines. The aims is to coordinate local IDDM registries, to promote the start of new registries in uncovered areas, and to standardize registration and data collection.