Context: In Zambia, most people know about sexually transmitted infections (STIs) and HIV/AIDS, but this knowledge has not translated into safer sexual practices. An estimated 16% of adults are HIV-positive, with the majority having acquired the infection through heterosexual contact. It is important to know whether characteristics such as wealth are correlated with extramarital sex among men, because men who have sex outside of marriage are key agents of heterosexual transmission of STIs and HIV. Methods: Data for analysis came from 1,239 married men who participated in the 2001-2002 Zambia Demographic and Health Survey. Multivariate analyses were performed to identify factors associated with men's extramarital sexual behavior, with a focus on wealth. Results: Overall, 19% of married men had had extramarital sex in the year prior to the survey; their mean number of partners was 1.3. Of the three proxies for wealth included in the multivariate analyses-education, occupation and household wealth index-none were associated with extramarital sex. Living in Southern and Western Provinces of Zambia was associated with significantly increased odds of extramarital sex (2.3 and 3.5, respectively); older age (0.4), older age at first sex (0.6-0.7) and living in Northern Province (0.4) were associated with significantly decreased odds of sex outside of marriage. Conclusions: Cultural norms specific to regions play an important part in sexual behavior. Socially defined sexual behavior patterns can shed light on extramarital sex and the spread of STIs, including HIV.