We analyzed incarcerated men's perceptions of and experiences with HIV testing. Interviews were conducted with 105 men, aged 18 to 29 years, in 4 states. Most men had received an HIV test while incarcerated because it was convenient or free or because they thought it was mandatory. At most sites, men believed they were HIV-negative because they never received test results. Some men did not know the diseases for which they had been tested. Some men avoided HIV testing outside prison because they lacked time, lacked resources, feared knowing the results, or perceived themselves to not be at risk. HIV testing programs for young men inside or outside prison should address barriers to HIV testing, communicate the meaning and extent of testing, and improve notification of those with HIV-negative results.