Objectives. We estimated the effects of high incarceration rates on rates of sexually transmitted infections and teenage pregnancies. Methods. We calculated correlations between rates of incarceration in state prisons and county jails and rates of sexually transmitted infections and teenage pregnancies for each of the 100 counties in North Carolina during 1995 to 2002. We also estimated increases in negative health outcomes associated with increases in incarceration rates using negative binomial regression analyses. Results. Rates of sexually transmitted infections and teenage pregnancies, adjusted for age, race, and poverty distributions by county, consistently increased with increasing incarceration rates. In the most extreme case, teenage pregnancies exhibited an increase of 71.61 per 100000 population (95% confidence interval [CI]=41.88, 101.35) in 1996 after an increase in the prison population rate from 223.31 to 468.58 per 100 000 population in 1995. Conclusions. High rates of incarceration can have the unintended consequence of destabilizing communities and contributing to adverse health outcomes.