The aim of this study was to examine the longitudinal predictors of buying and selling sexual services among youths in a high-income country. We used data from Switzerland (target sample: N = 1675 children, 52% male), where no prior studies have examined the trading of sexual services among representative samples of youths. Selling and buying sexual services were measured using novel, three-item measures at age 17. The predictors were measured at ages 13 and 15. In the regressions, multiple imputation was used to treat the missing values. Two-year point prevalence estimates of selling sexual services were 2.5% for females and 1.5% for males. Prevalence estimates of buying sexual services were 0.0% for females and 5.4% for males. Findings from logistic regressions revealed some support for prior findings from cross-sectional studies in high-income countries. New findings included evidence for prospective relations of having a disability, low generalized trust, and endorsing masculinity norms with trading sexual services. Follow-up models showed that the relations between pornography consumption and victimization with selling sexual services were gendered and stronger for females than for males.