This article analyzes the role of religious involvement and religious beliefs in the prevalence and frequency of smoking and alcohol consumption. This was a cross-sectional, population-based study. In 2005, we conducted door-to-door interviews with 383 people, aged 18 years or more, randomly selected from the "Paraisopolis" shantytown in São Paulo, Brazil. Four regression models were created to explain the relationships among religious involvement, tobacco and alcohol use, controlling for demographic, social, and psychobehavioral factors. High religious attendance was associated with less alcohol use, alcohol abuse, tobacco use, and combined alcohol/tobacco use, as well as less days consuming alcoholic beverages per week, controlling for confounding factors. Additionally, high nonorganizational religious behavior was associated with less tobacco and combined alcohol/tobacco use. Religiosity plays an important role in the control of alcohol and tobacco use in a shantytown setting; further management initiatives in the area should consider this issue. The study's limitations are noted.