OBJECTIVE: To examine the relationship between socioeconomic status (SES), risk factors for HIV infection and HIV status in an urban population with high prevalence of HIV infection in sub-Saharan Africa. METHODS: Cross-sectional population survey of adults from the city of Kisumu, Kenya, in 1996. Around 1000 men and 1000 women aged 15-49 years were interviewed using a structured questionnaire, and most gave a venous blood sample for HIV testing. SES was represented by a composite variable of educational status, occupation and household utilities. Multiple regression was used to examine whether SES was associated with HIV infection or with risk factors for HIV infection. RESULTS: Human immunodeficiency virus prevalence was 19.8% in males and 30.2% in females. Higher SES was associated with a more mobile lifestyle, later sexual debut and marriage among both sexes, and with circumcision among men aged 25-49 and condom use among women aged 25-49. Higher levels of alcohol consumption were associated with an increased risk of HIV infection and were more common amongst those of higher SES. HSV-2 infection was strongly associated with an increased risk of HIV infection and was more common among those of lower SES. HIV was associated with a lower SES among females aged 15-24 whereas in males aged 15-24 and females aged 25-49 there was some indication that it was associated with higher SES. Among males aged 25-49 there was no association between HIV infection and SES. CONCLUSIONS: Risk of infection was high among groups of all SES. Risk profiles suggested men and women of lower SES maybe at greater risk of newly acquired HIV infection. New infections may now be occurring fastest among young women of the lowest SES.