This article reports on a combined family-based substance abuse and HIV-prevention intervention targeting families with 13-14-year-old children in Bangkok, Thailand. Families (n = 340) were randomly and proportionally selected from 7 districts in Bangkok with half randomly assigned to an experimental or control condition. Families in the intervention condition were exposed to 5 interactive booklets about adolescent substance use and risky sexual behavior. Trained health educators followed up by phone to encourage completion of each booklet. Primary outcomes reported in this article include whether the intervention increased the frequency of parent-child communication in general or about sexual risk taking in particular as well as whether the intervention reduced discomfort discussing sexual issues. The authors also tested to see whether booklet completion was associated with communication outcomes at the 6-month follow-up. Multivariate findings indicate that the intervention had a significant impact on the frequency of general parent-child communication on the basis of child reports. The intervention had a marginal impact on the frequency of parent-child communication about sexual issues on the basis of parent reports. Booklet completion was associated with reduced discomfort discussing sex and was marginally associated with frequency of parent-child discussion of sex on the basis of parent reports only. These findings indicate that a family-based program can influence communication patterns.