The current study examined the protective effect of parenting-adolescent communication about sex on four risky sexual behaviors (age of onset of sex, number of sex partners, condom use, and STDs) among youth, framed by the Theory of Planned Behavior. It also tested for potential mediation effects between parent-adolescent communication and risky sex measures by sexual cues, date rape attitudes, and acceptance of dating violence in a sample of 2,245 college students from Japan, Slovenia, Spain, and the United States. Results provided evidence of a weak effect of parent-adolescent communication about sex on risky sexual behaviors across samples. A number of cultural influences were also found in the effects by mediators: sexual cues predicted risky sexual behaviors only in the Japanese sample; date rape attitudes was a predictor in the American and Slovenian samples; acceptance of dating violence predicted more risky sexual behaviors only in the American sample; and no significant effects were found in the Spanish sample. Several competing explanations were examined in the discussion to better understand the complex and dynamic interaction between parents and their adolescents as well as the role of culture. More studies are needed to better understand the associations between parent-adolescent communication about sex and risky sexual behaviors.