With young men who have sex with men (YMSM) continuing to be disproportionately affected by the HIV/AIDS epidemic in the U.S., secondary prevention efforts with this population take on increasing significance. We surveyed 200 HIV-positive YMSM (ages 16-24, 66% Black, 18% Latino, 7% White, 7% Multiracial/Other) recruited from 14 HIV primary care sites to examine associations of unprotected anal intercourse (UAI) and partner HIV status with endorsement of serosorting, sexual positioning, and viral load beliefs. Proportions of participants engaging in UAI one or more times during the past three months were consistent across type of UAI (insertive or receptive) and partner status. Belief that an undetectable viral load reduces infectiousness was significantly associated with insertive UAI (p < .05) and receptive UAI (p < .05) with HIV-negative or unknown status partners and receptive UAI with HIV-positive partners (p < .01). Endorsement of belief in serosorting was significantly associated with receptive UAI (p < .01) and insertive UAI (p < .05) with HIV-positive male partners. Implications for sexual behavior and risk reduction beliefs in this population are discussed.