Fitting a Poisson model to national data on the incidence of type 1 diabetes mellitus (T1DM) under 5 years (1993-95) and to age-specific incidence data from three different German regions (age groups 0-4, 5-9, 10-14, 15-19 years, 1988-1995), national age-specific incidences of T1DM in childhood were estimated. From these the age-standardized national incidence and prevalence were derived for age groups 0-15 and 0-19 years. In 1993-95 the age-standardized national incidences (95% CIs) in the age groups 0-14 and 0-19 years were 14.2 (12.9-15.5) and 17.0 (15.2-18.8) per 100,000 person-years, respectively. The respective national prevalences were 86.7 (83.4-90.0) and 140.2 (134.3-146.1) per 100,000 persons. These estimates of the national incidence and prevalence of T1DM for the mid-1990s were about twofold higher than estimates from the former Eastern Germany in the late 1980s. This striking high frequency of T1DM in Germany has an important impact on clinical and economic aspects of diabetes care in childhood and adolescence.