Young gay, bisexual, and other men who have sex with men (YMSM) under age 30 in New York City are at high risk for acquiring HIV. Using the theoretical framing of fundamental causes, this analysis examined the extent to which sociodemographic factors (race/ethnicity, perceived familial socioeconomic status [SES], U.S.-born status, and sexual orientation) explain the likelihood that HIV-negative YMSM ages 18 and 19 engage in unprotected sexual behavior, which may place them at risk for serconversion. Data were drawn from the baseline (Wave 1) assessment of a cohort study (N=592) collected between July 2009 and May 2011. The sample consisted predominantly of racial/ethnic minority YMSM (70.8%). A high level of association was demonstrated for each of the demographic factors with unprotected sexual behaviors. Multinomial logistic regression analyses were undertaken to examine associations between demographic covariates with the likelihood of engaging in unprotected sexual behaviors with male partners (any unprotected anal intercourse, as well as unprotected receptive anal, insertive anal, and receptive oral intercourse) irrespective of partner serostatus, in the month prior to assessment. U.S-born status and perceived socioeconomic status consistently were significant in differentiating risk behaviors. Being born outside the U.S. and perceiving a lower SES was associated with greater levels of risk. These findings suggest that efforts to address the disproportionate burden of HIV disease among YMSM in the United States must not focus solely on issues of race/ethnicity, but must be tailored and targeted to low SES and foreign-born young gay and bisexual men. It is posited that these demographic factors may lead to disproportionate levels of psychosocial burdens, which engender risk.