We evaluated the association between indicators of fetal growth and hospitalization with infectious disease during childhood in a cohort of 10,400 newborns. The cohort was based on children born to mothers who at about 36 weeks of gestation attended the midwife centres in Odense and Aalborg, Denmark for a routine examination. Women were recruited to the study from April 1984 to April 1987. After linkage with the National Hospital Registry, the first hospitalization with infectious disease from 6 months up to 12 years of age was identified. The cumulative incidence of hospitalization with infectious disease during follow-up was 18.9%. Preterm birth was associated with an increased risk of being hospitalized with infections during childhood (incidence rate ratio: 1.67, 95% CI: 1.33-2.10); low birth weight had a similar association, but only in preterm birth. Reduced birth length related to the head was correlated with an increased risk of hospitalization with infections. The effect of gestational age was mainly seen in the period close to the time of birth, but the children who were short at birth appeared to remain at increased risk throughout the age interval under analysis. In conclusion, the study suggests that preterm birth was the main factor underlying the association between low birth weight and the increased risk of hospitalization with infectious disease during childhood. However, it could not explain the increased risk in children who were short at birth.