Diagnostic and socio-demographic changes for children experiencing multiple hospital admissions (three or more) before the age of two years in two whole-year birth cohorts five years apart-1980 and 1985-are reported. The increase in multiple admissions between 1980 and 1985 was distributed evenly throughout the diagnostic groups. Although a disproportionate increase in admissions per child for asthma was noted, the results suggest that the increase accounts for only a small proportion of the total increase. A marked trend to earlier age of first admission is reported. Low-birthweight infants, infants of young mothers and infants from deprived areas of the city are overrepresented in the multiple admission groups in both cohorts. There was a marked increase in the proportion of low-birthweight infants in the multiple admissions group between 1980 and 1985 compared with a decrease in the percentage of low-birthweight infants in the control group over the same period. The study results are discussed with particular reference to the unexplained increase in early childhood admissions.