Is there a link between household income and income stress, and risky sexual behaviour of young people? Anecdotal and qualitative evidence suggests this may be the case, but there is little quantitative research measuring this relationship. We use two waves of new data from the Cape Area Panel Study to investigate this link for 2,993 African and coloured youths aged 14 to 22 in 2002. In the process, we discuss one type of research design that could allow for a causal interpretation of the effect of income poverty on HIV risk. This design plausibly separates out the effect of income stress from the effect of living in a poor household by comparing behaviours across households with and without negative economic shocks, conditional on baseline income. Our results indicate that females in poorer households are more likely to be sexually active in 2002 and more likely to sexually debut by 2005. In addition, girls in households experiencing negative economic shocks are more likely to reduce condom use between 2002 and 2005. However, they are less likely to have multiple partners in 2002 or have transitioned to multiple partners by 2005. Males who experienced a negative shock are more likely to have multiple partners. Despite the tight research design for assessing shocks, the findings on the impacts of shocks do not generate clear recommendations for policy. There appears to be no systematic difference in condom use at last sex by household income levels or income shocks.