In view of experimental and clinical findings, it was predicted (Dörner, 1973 and 1976; Dörner and Mohnike, 1973 and 1977) that a preventive therapy of diabetes mellitus may be possible by preventing hyperinsulinism in perinatal life by means of prevention of hyperglycaemia in pregnant women and overnutrition in newborns. Meanwhile, this prediction appears to have been realized. Thus, the prevalences of diabetes mellitus in children, who were born in Berlin/GDR over the past decade, were found to be significantly decreased as compared to those born between 1962 and 1972. On the other hand, the children born in Berlin/GDR between 1962 and 1972 displayed a significantly higher prevalence of diabetes mellitus as compared to those born between 1957 and 1961. The decreasing prevalence of childhood-onset diabetes over the past decade has been apparently achieved by systematic prevention of hyperglycaemia and impaired glucose tolerance in pregnant women and overnutrition in newborns. These findings suggest that a preventive therapy of diabetes mellitus--even of insulin-dependent childhood-onset diabetes--is possible by preventing hyperinsulinism in the foetus and newborn during differentiation and maturation of the neuroendocrine central nervous-pancreatic system.