Modern evidence on the post-weaning benefits of early-life breastfeeding is mixed. We provide novel evidence on the nature and reach of these benefits in a historical setting, drawing on a rich new longitudinal dataset covering nearly 1,000 children from the Foundling Hospital, an orphanage in turn-of-the-century London. We find that even after the cessation of breastfeeding, ever-breastfed status reduced mortality risk and raised weight-for-age in infancy, that exclusive breastfeeding conferred additional benefits, and that breastfeeding duration had little impact. We also find a U-shaped pattern in weight-for-age by time since weaning, indicating a deterioration in health shortly after weaning, followed by a recovery. The early post-weaning advantages associated with breastfeeding, however, did not persist into mid-childhood. This indicates that any protective effects of earlier breastfeeding attenuated with age, and suggest a strong role for catch-up growth. Thus, this study contributes to the data and empirical settings available to explore the relationship between infant feeding and post-weaning health, and helps shed light on the contribution of changing breastfeeding norms to trends in health in twentieth-century Britain.