This paper attempts to identify some factors associated with extramarital sex by men in the Mbeya region of Tanzania using data from a survey conducted in 2003/2004. The choice of Mbeya region was prompted by the fact that it has been found by previous studies to be one of the regions with the highest HIV prevalence rate in Tanzania. Correlates of extramarital sex that were considered include current age, education, residence, age at first sexual intercourse, age at first marriage and sex before marriage. A bivariate analysis of the survey data, which comprised a sample size of 568 married men aged between 15 and 62 years revealed statistically significant association between extramarital sex with current age, education, age at first intercourse and sex before marriage. The effect of these variables was tested through a multivariate logistic regression analysis and all the four independent variables were found to be statistically significant predictors of extramarital sex in Mbeya region.Faculty of Arts and Social Sciences, University of Dar es Salaam through Sida/SAREC Core Support