Lead is a neurotoxin with developmentally harmful effects in children. In the United States, over half the current flow of lead into the atmosphere is attributable to lead-formulated aviation gasoline (avgas), used in a large fraction of piston-engine aircraft. Various public interest firms have petitioned the EPA to find endangerment from and regulate lead emitted by piston-engine aircraft, though the EPA has so far ruled against such petitions. To address an EPA request for more evidence, we construct a novel data set that links time and spatially referenced blood lead data from over a million children to 448 nearby airports in Michigan. Across a series of tests, and adjusting for other known sources of lead exposure, we find that child blood lead levels (1) increase dose-responsively in proximity to airports, (2) decline measurably among children sampled in the months after 9/11, (3) increase dose-responsively in the flow of piston-engine aircraft traffic, (4) increase in the percentage of prevailing wind days drifting in the direction of a child’s residential location, and (5) behave intuitively and significantly when considering two-way and three-way interactions of our main treatment variables. To quantify the policy relevance of the results we provide a conservative estimate of the social damages attributable to avgas consumption. Damages are at least $10 per gallon, which can be compared to a pump price of about $6 per gallon.