Among the estimated number of persons living with HIV at the end of 2006, 46.1% (1,715.1 per 100,000 population) were black, 34.6% (224.3 per 100,000) were white, 17.5% (585.3 per 100,000) were Hispanic, 1.4% (129.6 per 100,000) were Asian/Pacific Islander, and 0.4% (231.4 per 100,000) were American Indian/Alaska Native. Males accounted for 74.8% of prevalent HIV cases (685.7 per 100,000). The greatest percentage of cases was attributed to male-to-male sexual contact, accounting for 48.1% overall (and 64.3% among men). High-risk heterosexual contact, defined as heterosexual contact with a person known to have, or to be at high risk for, HIV infection (e.g., an injection drug user) accounted for 27.6% of prevalent cases overall (12.6% of cases among men and 72.4% of cases among women). Injection drug use (IDU) accounted for 18.5% of total cases (15.9% of cases among men and 26.3% of cases among women). The remainder of cases were attributed to men who reported both male-to-male sexual contact and IDU (5.0%) or whose transmission category was classified as other (0.8%; including hemophilia, blood transfusion, perinatal exposure, and risk factors not reported or not identified). Overall, an estimated 232,700 (21.0%) persons living with HIV infection had not been diagnosed as of the end of 2006.