We aim to apply critical incident methodology to details of respondents' last sexual encounter to provide contextualized data on sexual behaviour and alleviate the problem of recall bias. In areas of Houston, Texas, registering high prevalence rates of syphilis, we elicited information from 400 men and women about the last time they had sex. Details of time, place, partner, activities, and situational circumstances were collected in street intercept interviews. Nearly 50% of men and 30% of women were drunk or high the last time they had sex, and more than one-quarter of last encounters occurred in hotel or motel rooms. Drug use was not related to condom use. Both men and women were more likely to use condoms with new than with more familiar sex partners; however, women were less likely than men to report condom use across all types of sexual activity, and particularly for anal sex. The findings are being used to design a syphilis prevention intervention in the study communities.