Significance Childhood lead exposure causes lifelong psychological problems, which may be more extensive than previously thought. In a sample of over 1.5 million people, we found that US and European residents who grew up in areas with higher levels of atmospheric lead had less adaptive personality profiles in adulthood (lower conscientiousness, lower agreeableness, and higher neuroticism), even when accounting for socioeconomic status. These effects were driven by participants ages 20 to 39. In a natural experiment, reductions of leaded gasoline in the United States following the 1970 Clean Air Act corresponded with increases in psychologically healthy personality traits. These results suggest that even low-level lead exposure may adversely impact personality traits, harming the well-being, longevity, and economic prospects of millions of people.