The present study considers the influence of the parent-child relationship on adolescent virginity status using data from two waves of the National Longitudinal Study of Adolescent Health. The authors examine how adolescents' perceptions of the quality of their parent-child relationships--and the varying levels of parental involvement in their lives--influences the likelihood of first sex among a sample of adolescent virgins living in biologically intact, two-parent families. The authors pose and test a conceptual model linking parent-child relationships to first sex via diminished actual and cognitive opportunities for sex. The results indicate that girls who enjoy a close relationship with their father are less likely to report first sex between study waves. No comparable direct relationship appeared for boys or with the mother-child relationship. Actual and cognitive opportunities--including dating and anticipation of guilt--corresponded with diminished likelihood of first sex and appeared to mediate the direct effect of the father-daughter relationship. (Contains 4 notes, 1 figure, and 5 tables.)