Background. Recent evidence suggests potential associations between birthweight and infant feeding history and risk of a variety of health outcomes during adulthood. Because studies may rely on self-reported birthweight and infant feeding history, it is important to assess the validity of this information. Methods. The authors compared birthweights reported by a sample of 538 women, 27-44 years of age, participating in the Nurses' Health Study II (NHSII) cohort, with birthweights recalled by their mothers and with those from state birth records. In addition, we compared participants' self-reported history of having been breastfed with their breastfeeding history reported by their mothers. Results. For birthweight, the correlation between reports by the cohort participants and by their mothers was high (Spearman r = 0.75). Compared with weights recorded on state birth records, correlations were 0.74 for reports by cohort participants and 0.85 for reports by their mothers. When comparing NHSII participants' self-report of ever having been breastfed with their mothers' report, sensitivity was 82% and specificity was 86%. For duration of breastfeeding, the Spearman correlation between mother and daughter reports was 0.74. In analyses stratified by four ethnic groups (African-American, Asian, Caucasian, and Hispanic) we observed substantial differences in distribution of birthweight and breastfeeding patterns; however, the degree of validity in reporting them was similar. Conclusion. The validity of self-reported birthweight and breastfeeding history by these middle-aged women appears to be high.