Evidence on the post-weaning benefits of early-life breastfeeding is mixed, and highly context-dependent. Moreover, this evidence is drawn almost exclusively from modern settings, limiting our understanding of the relationship between breastfeeding and subsequent health in the past. We provide novel evidence on the nature and reach of these post-weaning benefits in a historical setting, drawing on a rich new longitudinal dataset covering nearly 1000 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 suggests a strong role for catch-up growth. 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.