Youth sex and relationship education programs aim to improve adolescent well-being by changing their knowledge, beliefs, and attitudes regarding sex and their health. However, there is a gap in existing research linking these cognitive targets to relevant behaviors, and a particular dearth of data on links with sexual behaviors. The current study tested longitudinal links between cognitive factors related to sex (attitudes about sex, normative beliefs, risk-avoidant intentions, and confidence in refusal skills) and outcomes of sexual behaviors (recent sexual encounters, number of sexual partners, and frequency of condom use). Data were drawn from three waves of data from a panel study of US high-school students and were analyzed using cross-lagged structural equation modeling. We hypothesized direct, reciprocal links between intentions and behaviors, but this hypothesis was not supported. Instead, more conservative attitudes about sex emerged as the most consistent prospective predictor of fewer sexual encounters and sexual partners, though with small effect sizes (βs = -.08 to-.131, ps < .05). Further, bidirectional interrelationships were observed among several of the cognitive and behavioral variables over time. These results highlight attitudes about sex as a potentially useful intervention target, but also suggest that sex and relationship education curricula and evaluations should consider multiple pathways of links between cognition and behavior. Continued research is needed on causal links between adolescents' sexual attitudes, knowledge, intentions, and behavior.