This paper uses retrospective event-history data covering a four-year period to examine the timing of exposure to HIV/AIDS education and social marketing condom promotion campaigns, relative to the timing of changes in sexual risk behaviour in Tanzania. Analysis of the event-history data shows that the process of exposure to AIDS education messages and exposure to brand advertising for Salama brand condoms was very different. While exposure to AIDS education was early and gradual, exposure to Salama brand condoms started later, but was much more rapid. After one year of advertising, over half of the target population had been reached by the Salama advertising campaign, mostly through newspapers, radio and television. During the study period, condom use increased from 15% at the beginning of 1993 to 42% at the end of 1996. Increases in condom use were driven both by men who became sexually active, and by men who were not yet protected, or not fully protected. The results further show that it is uncommon for men who adopted condom use to return to more risky behaviour, which suggests that behaviour change in the study population is permanent.