The vast majority of high schools require some form of sex education. Despite numerous concerns about the efficacy of abstinence-only education programs and their failure to demonstrate a reduction in the onset of teenage sexual activity, such curricula remains widespread in U.S. public schools. One resource in formal sex education is health textbooks. Six widely used high school health textbooks were investigated. Through qualitative content analysis of the written material, a shared emphasis on abstinence was identified, specifically in relation to premarital relationships, decision-making, and risk prevention. Textbooks emphasize that marriage is the only appropriate place for people to have sex, aim to instruct teens on how to make responsible decisions and how to refuse engaging in deviant behavior, and stress that sex is a high-risk activity that teens should avoid in favor of abstinence. Using the data from these high school health textbooks, I develop a theory of patronizing exclusivism to explain the implicit and explicit messages about abstinence and identify six primary features: perpetuation of the stereotypical ideal family, denial of demographic realities, assumption that teens are impulsive, conflation of sex with morality, encouragement of stigma of the sexually active, and promotion of sex negativity. Promotion of sex negativity is the root strategy and facilitates the implicit and explicit messages about abstinence in high school health textbooks. The theory of patronizing exclusivism has implications relevant to dialogue about how sex education should be taught and what should be included.