BACKGROUND: Studies on the association between breastfeeding and infections in children beyond the first year of life reveal conflicting results. In a population-based birth cohort, we investigated whether the duration of breastfeeding was associated with the number of hospitalizations due to infection and symptoms of infection at home. METHODS: In the Odense Child Cohort, text message questionnaires were used to register information on breastfeeding (weekly until end of weaning) and symptoms of infection (biweekly; 12–36 months of age). Hospitalization data were obtained from the Danish National Patient Registry. RESULTS: Of the 1087 invited, 815 mother-infant pairs were included. The median duration of any breastfeeding was 7.6 (interquartile range: 3.5–10.4) months and of exclusive breastfeeding was 2.1 (interquartile range: 0.7–4.4) months. Hospitalization due to infection was seen in 207 (25.4%) infants during the first 3 years of life. The adjusted incidence rate ratio (IRR) for hospitalization due to any infection decreased with a longer duration of any breastfeeding (adjusted IRR: 0.96; 95% confidence interval 0.93–0.99; P, .001). The strongest associations between the duration of any breastfeeding and hospitalizations due to infection were found within the first year of life, for lower respiratory tract infections, and other infections (P # .05). For infants exclusively breastfed, the adjusted IRR for hospitalization was 0.88 (95% confidence interval: 0.80–0.96; P = .006). No protective associations were present between breastfeeding and infection symptoms registered at home from ages 12 to 36 months. CONCLUSIONS: The results suggest that increased duration of breastfeeding, especially exclusive breastfeeding, protects against infections requiring hospitalization in the first year of life but not hospitalizations or symptoms of infection at home beyond the first year.