A large literature documents a strong correlation between health and educational outcomes. In this paper we investigate the role of cognitive ability in the health–education nexus. Using NLSY data, we show that cognitive ability accounts for roughly one quarter of the association between schooling and health. Both schooling and ability are strongly associated with health at low levels but less related or unrelated at high levels. Estimates treating schooling as endogenous to health suggest that most of the correlation between schooling and health is attributable to unobserved heterogeneity, except possibly at low levels of schooling for individuals with low cognitive ability. An implication is that policies which increase schooling will only increase health to the extent that they increase the education of poorly-educated individuals; subsidies to college education, for example, are unlikely to increase population health.