Over 11,000 children belonging to population-based cohorts were followed through infancy in the city of Pelotas, Brazil, in 1982 and 1993. Our objective was to measure the incidence of hospital admissions and the association with birthweight and family income, comparing differentials between the two studies. Approximately 20% of infants were hospitalized at least once, rates being higher among boys. Hospitalization due to diarrhea dropped from 6% to 3% and was more commom among the poor. Birthweight was inversely associated with both diarrhea specifically and all causes of hospitalization. Children with low birthweight or from low-income families (less than three times the minimum monthly wage) were approximately three times more likely to be hospitalized than those with adequate birthweight or higher incomes. Hospitalization was still common a decade later, especially among low birthweight and poor infants.