Relationships between body size and sexuality outcomes vary by participant demographics. Lack of sample diversity has limited generalizability. The authors hypothesized that body size would influence sexual activity, moderated by multiple social categories. Racially diverse heterosexual participants (n = 7,398) reported body size, sexual activity status, and number of sexual partners. Age interacted with body mass index (BMI) to predict sexual activity status. Gender, age, race, and marital status did not interact with BMI to predict number of partners. Contrary to prevalent media depictions, higher BMI may increase likelihood of sexual activity during young adult years, while decreasing likelihood of sexual activity in adults over 25.