Although incarceration rates have risen sharply since the 1970s, medical sociology has largely neglected the health effects of imprisonment. Incarceration might have powerful effects on health, especially if it instills stigma, and it could provide sociologists with another mechanism for understanding health disparities. This study identifies some of incarceration's direct and indirect effects and rigorously tests them using the National Longitudinal Survey of Youth. It finds that incarceration has powerful effects on health, but only after release. A history of incarceration strongly increases the likelihood of severe health limitations. Furthermore, any contact with prison is generally more important than the amount of contact, a finding consistent with a stigma-based interpretation. Although this relationship is partly attributable to diminished wage growth and marital instability, the bulk of the effect remains even under the most stringent of specifications, including controls for intelligence and the use of fixed effects, suggesting a far-reaching process with a proliferation of risk factors. The study also finds that incarceration contributes only modestly to racial disparities, that there are few synergistic interactions between incarceration and other features of inequality, including schooling, and that the evidence for a causal effect is much weaker among persistent recidivists and those serving exceptionally long sentences. These study findings are inconsistent with recent speculation; nevertheless, incarceration is an important addition to sociology's research agenda. Exploring incarceration could lead to, among other things, a fruitful synergy among studies on fundamental causes, stigma, and stress.