Parental sex education might promote healthy sexual behavior among adolescents, but some parents assume that family communication about sex will lead to sexual activity. Family sex communication has been studied with a limited range of adolescent sexual behaviors but not sexual fantasy or desire. Two measures of family sex communication were compared and examined in relation to measures of sexual fantasy, desire, attitudes, and behavior among a sample of 522 females and males in their late adolescence. An expanded range of sexual behaviors was assessed. Family sex communication was not associated with level of sexual fantasy, desire, attitudes, or most sexual behaviors. Causal inferences cannot be made, but parents might consider talking openly with their children about sexual matters without fearing that such communication will ignite their sexual desire or prompt sexual behavior. (Contains 3 tables.)