Nearly 70 registries from more than 40 countries have collected and published incidence data of childhood Type 1 (insulin-dependent) diabetes mellitus up to the end of the 1980s. The majority of incidence data comes from regions of high incidence i. e. from Europe and North America. All these published data facilitate the descriptive comparison of incidence and variation of the occurrence of Type 1 diabetes roughly throughout the northern hemisphere. The aim of this paper is to review and compare the most recent epidemiology data on the incidence of Type 1 diabetes among children under the age of 15 years. A clear difference in incidence appeared between northern and southern hemisphere with no countries below the equator having an incidence-greater than 15.0 per 100,000. In contrast above the equator the disease is common. Between continents the variation in incidence showed that the lowest incidences were found in Asia, followed by Oceania (Australia and New Zealand), South and North America, and the highest rates were in Europe. The incidence varied from 0.6 per 100,000 in Korea and Mexico to 35.3 per 100,000 in Finland showing prominent worldwide variation in incidence of Type 1 diabetes. The largest intracontinental variation in incidence appeared in Europe, varying from the highest in Finland to the lowest (4.6 per 100,000) in northern Greece. The highest incidence in the world was in northern Europe, but within the continent scale there were some striking exceptions from the overall level of incidence. In Iceland, the northern-most island nation in Europe, the incidence is only one-half of that in Norway and Sweden and one-third of that in Finland. In contrast, in Sardinia in southern Europe the Type 1 diabetes incidence is virtually the same as in Finland, three times higher than overall incidence in Europe. Large variation was also seen in small ''pockets'' of countries, particularly in the Baltic sea region. The worldwide variation in incidence reflects the distribution of ethnic populations and demonstrates the importance of the differential genetic susceptibility between populations.
