A retrospective epidemiological study using primary data sources and external validation was made to assess the incidence of childhood diabetes (0-14 yr) over a ten-year period. The degree of ascertainment was 96.2 per cent. Age-specific incidence rates increased until puberty with peak incidence in girls at 10 year and in boys at 13 year. There was a seasonal variation of onset with peaks in autumn and winter. The yearly incidence rates showed an increasing trend, the incidence in 1987 (8.7/100,000) was 2.3 times higher than in 1978. The rise in incidence was not continuous, incidence rates were similar in the years 1978-79, 1980-84 and 1985-87, but relatively sharp increases could be observed in 1980 and in 1985 which were mainly due to increases in incidence of the age group 5 to 9 years. Dynamic changes have taken place in the incidence of childhood diabetes in Hungary between 1978 and 1987, but it is not known whether the increases can be regarded as epidemics or parts of a discontinuous trend.