This cross-sectional study examined the relationships between ethnicity, sex, risk group, and virus load in human immunodeficiency virus type 1 (HIV-1) antiretroviral-naive patients. HIV-1 RNA levels were measured in 322 patients attending St. Thomas' Hospital between May 1997 and February 1999. By univariate analyses, only clinical status and CD4(+) cell count were related to virus load. In multivariate analysis, variables independently related to virus load were CD4(+) cell count (P=.001), being black African (P=.001), having a nonsexual risk for HIV infection (P=.03), and having AIDS (P=.05). Neither sex nor age was a significant predictor of initial virus load after adjusting for other variables. For a given CD4(+) cell count, black Africans and people who contracted HIV nonsexually presented with a virus load lower than that of patients in other groups. Because virus loads may need to be interpreted differently according to ethnicity, this may affect decisions on when to initiate antiretroviral therapy and how to interpret clinical trial results.