Parent–child communication about sex is an important reproductive health outcome. Consistent, positive perceptions of communication by parents and children can promote behavioral outcomes such as delaying sexual debut and increasing contraceptive use. The authors investigated whether exposure to messages from the Parents Speak Up National Campaign (PSUNC), a social marketing campaign to promote increased parent–child sexual communication, led to increased children's self-reports of communication. Also, the authors examined whether PSUNC message exposure increased agreement about communication between parents and their children. In a randomized experimental design, the authors surveyed children of parents exposed and not exposed to PSUNC messages. Parents and children completed online instruments asking matched questions about sexual attitudes, beliefs, and communication. The authors matched 394 parents and children for analysis. They used ordinal logistic regression modeling and kappa statistics. Children of parents exposed to PSUNC messages were more likely to (a) report sexual communication than were those not exposed and (b) agree with their parents about extent and content. Parent–child pairs of the same gender, younger pairs, and non-White pairs were more likely to agree. Overall, PSUNC message exposure appears to have promoted more extensive sexual communication. Future research should examine behavioral mechanisms and message receptivity among subgroups of parents and children.