Breastfeeding has been linked to a lower risk of overweight and asthma in children, however the results of previous studies are conflicting and controversy remains. An important gap in the current knowledge on the association between breastfeeding and overweight and asthma is whether and how the association changes with age of the child. These topics were investigated in the Prevention and Incidence of Asthma and Mite Allergy (PIAMA) study. This is a prospective birth cohort study of 3963 Dutch children from the general population followed from birth to 8 years of age. Data were mainly collected by yearly questionnaires. At 4 and at 8 years a subgroup of the total study population was invited for a medical examination. In the PIAMA study, 82% of the children was breastfed and about one third of the children was breastfed for more than 16 weeks. At 8 years of age, 14.5% of the children in the total study population was overweight and 13.8% had asthma. Breastfed children had a lower BMI at 1 year of age compared to non-breastfed children. Longitudinal analyses showed that children breastfed for more that 16 weeks had a significantly lower BMI from 1 to 7 years of age than non-breastfed children. However, when BMI at 1 year of age was taken into account, breastfeeding for more than 16 weeks was not associated with BMI from 1 to 7 years of age. Breastfed children had a more healthy eating pattern at 7 years of age compared to non-breastfed children, independently of maternal characteristics. However, the healthier eating pattern could not explain the lower overweight prevalence among breastfed children compared to non-breastfed children. Breastfeeding for more than 16 weeks was significantly associated with a lower asthma prevalence from 3 to 8 years of age compared to no breastfeeding. The associations were similar in children from allergic and non-allergic parents. Also, children breastfed for more than 16 weeks were less likely to be sensitised to inhalant allergens, but breastfeeding was not related with ...