Seventeenth-century UK experienced an epidemic of the newly recognised disease rickets, its nutritional and environmental causes then unknown. This is evident from parish burial registers, the London Bills of Mortality, and contemporary medical descriptions and treatments. Rickets appeared to be killing 2-8 per cent of urbanites, especially wealthy children. Rickets emerged as a threat to child health in early modern UK as a result of coal dependency and climate, and social differences in infant and child feeding. Physicians investigating rickets showed concern for rich children's diets. Lack of breastfeeding promoted calcium deficiency among wealthy infants, while poorer children's meagre childhood diet retarded recovery. The seasonality and age incidence of rickets deaths corroborate this diagnosis, but after 1700 rickets deaths dwindled even as medical treatises and osteological evidence suggest rickets morbidity increased. Chronology and share of mortality of other causes relating to rickets morbidity are considered: scurvy, hydrocephalus and whooping cough.