Exposure to smoggy days is a common part of urban life, but can be avoided by vulnerable populations with municipal investment in warnings. This paper provides the first evidence on the long-term effects of early exposure to smog. Variation comes from exposure to the Great London Smog of 1952. Affected cohorts are tracked for up to sixty years using the Office of National Statistics Longitudinal Study. Exposure to the four day smog reduced the size of the surviving cohort by 2% and caused lasting damage to human capital accumulation, employment, hours of work, and propensity to develop cancer.