We sought to determine the prevalence and correlates of self-reported HIV testing among inmates in correctional centers in Ontario, Canada. A cross-sectional survey was conducted with a stratified random sample of 597 male and female adult inmates. The participation rate was 89%. Descriptive statistics and multiple logistic regression were used to analyze HIV testing. Fifty-eight percent had ever been tested, and 21% had voluntarily tested while incarcerated in the past year. Having ever been tested was more common among those at risk for HIV through injection drug use (IDU) or sexual behavior. Testing while incarcerated in the past year was independently associated with being single (OR = 2.6), frequent IDU (OR = 4.0), not having casual sex partners prior to incarceration (OR = 0.53), a history of hepatitis (OR = 2.4), previous HIV testing (OR = 3.7), a close relationship with an HIV-positive person in the outside community (OR = 1.7), knowing an HIV-positive person inside (OR = 2.7), a perceived chance of being infected during incarceration (OR = 2.2), and support of mandatory testing (OR = 2.0). The predominant motivations for testing while incarcerated were IDU or fears of infection inside, possibly through contact with blood, during fights, or even by casual contact. Voluntary HIV testing in prison should be encouraged, and inmates should receive appropriate counseling and information to allow realistic assessment of risk.