Little is known about the relationship among body weight, body image, and HIV/AIDS sexual risk behaviors. We examined this issue in a midwestern U.S. metropolitan area community sample of 316 men who have sex with men, a group at relatively high risk for HIV/AIDS. All data were self-reported by questionnaire using standard items to assess current body image, height and weight, and HIV/AIDS sexual risk behaviors. Logistic regression models were used to estimate cross-sectional associations. Forty-nine (15%) of the 316 men were classified as obese, and 56 (18%) had unsafe sex in the past three months. Normal weight or overweight men were 3.6 times more likely than obese men to have had unsafe sex, after adjusting for differences in body image and age. Men with better body image were 1.4 times more likely than men with lower body image to have had anal sex, after adjusting for differences in body weight and age. Non-obese men were no more or less likely than were obese men to have engaged in anal sex or in any sex in the past three months. This is the first study showing a positive relationship between below-obese body weight and unsafe sex and between better body image and anal sex in men who have sex with men. Future research should investigate these novel findings, perhaps using other study designs and data collection tools with less measurement error. Advances in knowledge about HIV/AIDS risk factors, including body weight and body image, could potentially contribute to more effective approaches to reducing this risk.