More than 1.2 million Swedish children born 1946-60 and enumerated in the 1960 population census were followed up with respect to mortality for the period of 1961-79. Thus the children were younger than 15 years at the start of the follow-up and their age of death varied between 1 and 33 years. More than 13,000 deaths were analysed. The purpose was to examine whether or not mortality differences by socio-economic group in childhood persist into adulthood. Mortality differences by childhood socio-economic group were studied for both children/adolescents (1-19 years old) and young adults (20-33 years old). Information about the adults' own occupational status was not available. Therefore, to allow a deeper analysis, another group of adults, whose mortality could be analysed by their own socio-economic group, was used as a comparison group. Among children and adolescents there was a clear socio-economic group difference in mortality. Children in families of non-manual workers had a significantly lower mortality than children in the families of manual workers. In particular this was the case for boys. Socio-economic differences in total mortality are evident also in the age between 20 and 33 years among men but it could not be demonstrated here that these are a result of childhood socio-economic group rather than achieved socio-economic group. However, the study indicates that some differences in childhood, to a certain degree and for some diagnoses, may persist into adulthood. Of particular interest may be a tendency for cardiovascular disease mortality to be elevated among sons and daughters of manual workers.(ABSTRACT TRUNCATED AT 250 WORDS)