Left- and right-handed individuals have different neurological wiring, particularly with regard to language processing. Multiple datasets from the United States and the United Kingdom show that lefties exhibit significant human capital deficits relative to righties. Lefties score 0.1 standard deviations lower on cognitive skill measures, have more behavioral problems, have more learning disabilities such as dyslexia, complete less schooling, and work in occupations requiring less cognitive skill. Most strikingly, lefties have 10-12 percent lower annual earnings than righties, much of which can be explained by observable differences in cognitive skills and behavioral problems. Lefties work in more manually intensive occupations than do righties, further suggesting their primary labor market disadvantage is cognitive rather then physical. I argue here that handedness can be used to explore the long-run impacts of differential brain structure generated in part by genetics and in part by poor infant health.