High rates of human immunodeficiency virus (HIV) infection among jail and prison inmates suggest that HIV prevention efforts should focus on incarcerated populations. Overcrowding, the high prevalence of injection drug use, and other high-risk behaviors among inmates create a prime opportunity for public health officials to affect the course of the HIV epidemic if they can remedy these problems. Yet, along with the opportunity, there are certain obstacles that correctional institutions present to public health efforts. The various jurisdictions have differing approaches to HIV prevention and control. Whether testing should be mandatory or voluntary, whether housing should be integrated or segregated by HIV serostatus, and whether condoms, bleach, or clean needles should be made available to the prisoners, are questions hotly debated by public health and correctional officials. Even accurate assessment of risk-taking within the institutions leads to controversy, as asking questions could imply acceptance of the very behaviors correctional officials are trying to prevent. Education and risk-reduction counseling are the least controversial and most widely employed modes of prevention, but the effectiveness of current prevention efforts in reducing HIV transmission in this high-risk population is largely undetermined.