Average annual rates of HIV diagnoses for specific transmission categories were calculated using race/ethnicity- and age-specific census data as the denominators. For example, the rate of cases among blacks with male-to-male sexual contact represents the number of cases among black MSM per 100,000 black males during 2001-2004. Blacks had the highest average rates for all transmission categories. For cases among MSM, the rate for blacks was 69.0 per 100,000, compared with 13.9 for whites, 37.8 for Hispanics, 8.2 for Asians/Pacific Islanders (A/PIs), and 12.1 for American Indians/Alaska Natives (AI/ANs). For cases among males reporting IDU, the rate for blacks was 26.9 per 100,000, compared with 1.7 for whites, 12.0 for Hispanics, 1.6 for A/PIs, and 2.7 for AI/ANs. For cases among males with high-risk heterosexual contact, the rate for blacks was 35.5 per 100,000, compared with 1.1 for whites, 10.9 for Hispanics, 2.3 for A/PIs, and 2.4 for AI/ANs. For cases among females reporting IDU, the rate for blacks was 14.2 per 100,000, compared with 1.0 for whites, 4.8 for Hispanics, 0.6 for A/PIs, and 2.2 for AI/ANs. For cases among females with high-risk heterosexual contact, the rate for blacks was 58.3 per 100,000, compared with 2.2 for whites, 15.0 for Hispanics, 2.8 for A/PIs, and 5.3 for AI/ANs.