Background: Most research linking weight status and timing of first sexual intercourse is cross-sectional in design, with few longitudinal analyses published to date. We examined associations between childhood weight status and subsequent onset of first sexual intercourse within a survival analytic framework, testing for differences among Hispanic, black, and white females and males. Methods: Data were drawn from 6379 child respondents of the 1979 National Longitudinal Survey of Youth aged 13 and older at last assessment. Cox proportional hazards regression models were estimated predicting age at first sexual intercourse from weight status during childhood without and with adjustment for correlated risk factors. Analyses were conducted separately by sex and race/ethnicity, with interactions among weight status, respondent sex, and race/ethnicity modeled in subsidiary analyses. Results: Overweight status predicted earlier sexual intercourse among Hispanic females, whereas obese status predicted delayed sexual intercourse among white males, both relative to peers of the same race/ethnicity with healthy weight. Underweight status predicted delayed sexual intercourse among Hispanic males relative to peers with healthy weight. Significant differences by sex and race/ethnicity were observed in tests of interactions. Conclusions: Findings document associations between childhood weight status and subsequent onset of first sexual intercourse, especially among Hispanic females and males and white males. Together, results highlight respondent sex and race/ethnicity as potential moderators and also unique risk for Hispanic females who were overweight as children, and who may benefit from early screening and education to delay sexual initiation to reduce risk of early unplanned pregnancy and sexually transmitted infections.