Mortality among 4740 diabetic men and women aged 35-55 years participating in the WHO Multinational Study of Vascular Disease in Diabetics has been studied. Ten of the original centres (Warsaw, Berlin, Havana, Arizona, Oklahoma, Hong Kong, Switzerland, London, Tokyo, Zagreb) were able to identify the life/death status of their study participants on 1 January 1983, giving an average follow-up period of six to seven years. All-cause mortality rates in males varied about threefold among the ten participating centres with the highest rates in Warsaw, Berlin and Havana and the lowest rates in Tokyo and Zagreb. All-cause mortality rates for females varied about fourfold with the highest rates in Warsaw and Oklahoma and the lowest rates in Tokyo. The proportion of deaths ascribed to circulatory disease varied among the centres ranging from 32% for males and 0% for females in Tokyo to 67% for males and 47% for females in London. There was an excess all-cause mortality in males compared to females for all centres except Zagreb. This excess also applied to circulatory diseases in general, ischaemic heart disease in particular and occurred in both insulin-dependent and non-insulin-dependent diabetic patients. Death rates for insulin-dependent diabetic patients were generally higher than those for non-insulin-dependent patients.