Since 2006, CDC has recommended routine, opt-out human immunodeficiency virus (HIV) screening for patients in health-care settings with a prevalence of undiagnosed HIV infection of ≥0.1%.1,2 Before September 2007, the Washington State Department of Corrections (WADOC) only provided HIV testing to inmates on request. In September 2007, WADOC began routine HIV opt-in screening in which inmates were notified that HIV screening would be performed during the prison intake medical evaluation if they consented. In March 2010, WADOC switched to a routine opt-out HIV screening model in which inmates are notified that HIV screening will be performed unless they decline. To assess the proportion of inmates screened and the number of infections diagnosed during the use of the three HIV testing policies, WADOC reviewed HIV testing data for male inmates undergoing intake medical evaluation during January 2006–December 2010. From January 1, 2006, to August 31, 2007, 5% of 12,202 incoming inmates were tested for HIV at their request during the intake medical evaluation, and three (0.50%) of those tested had newly diagnosed HIV infection. From September 1, 2007, to March 15, 2010, 72% of 16,908 inmates agreed to opt-in HIV screening, and 13 (0.11%) tested positive for HIV. From March 16, 2010, to December 31, 2010, 90% of 5,168 inmates agreed to opt-out HIV screening, and six (0.13%) tested positive for HIV. Compared with routine opt-in HIV screening, opt-out HIV screening was associated with a greater proportion of inmates tested, without decreasing the rate of case detection.