Homeless people are one of the most vulnerable with regard to HIV transmission. However, most research on this population has been carried out on samples from health clinics. We surveyed 390 homeless people in Houston at a day shelter with regard to their HIV/AIDS knowledge and risk behaviours. The sample was 76% African-American, 11% Euro-American, with small numbers of Latin-Americans, Native-Americans and Asian-Americans: half were born in Texas, and 92% were male. Data indicated that HIV/AIDS knowledge was higher in those who were at higher behavioural risk, although the direction of causality in these cross-sectional data cannot be inferred. African-Americans were at slightly higher risk. Compared with previous clinic samples, this sample was older and a higher number (one-third) slept the last night outside. Eighty per cent had had an HIV test. Condom use was low with both males and females most commonly not reporting using condoms although more than half had had sexual contact in the past month. Multivariate analysis indicated that ethnicity and HIV/AIDS knowledge were independent predictors of risk behaviour. Lifetime risks included one-third who had injected drugs land shared needles), and nearly 10% had had sex with someone they knew to be HIV seropositive. Lack of future time perspective rather than level of knowledge may be a barrier to reducing HIV risks, and the data are discussed in terms of policy implications and homelessness.