Background: This study examined 3 hypotheses: (1) adolescents who perceive maternal disapproval of sexual activity will initiate sexual intercourse later than other adolescents; (2) adolescents who feel highly connected to their mothers will initiate sexual intercourse later than others; and (3) adolescents who perceive maternal disapproval of sexual intercourse are more likely than others to experience high levels of connectedness to their mothers, and to have mothers who state strong disapproval and talk more frequently with them about sex. Design/Setting: The National Longitudinal Study of Adolescent Health (Add Health), a longitudinal study of US students in grades 7 through 12. The Add Health core in-home sample consisted of 12 105 students who completed in-school and in-home surveys at wave 1). Members of this sample completed a second in-home survey 9 to 18 months later at wave 2. Participants: Wave 1 and wave 2 in-home surveys were completed by 3322 core sample members who had reported being virgins at wave 1, and had resident mothers who completed wave 1 surveys. Main Outcome Measures: Time to first sexual inter-course, adolescents' wave 2 reports of month/year of first sexual intercourse. Results: Adolescents' perceptions of maternal disapproval and high levels of mother-child connectedness were directly and independently associated with delays in first sexual intercourse. Adolescents were most likely to perceive maternal disapproval if their mothers reported strong disapproval and if they reported being highly connected to their mothers. Conclusion: Perceived maternal disapproval of sexual intercourse, along with mother-child relationships characterized by high levels of warmth and closeness, may be important protective factors related to delay in adolescents' first sexual intercourse.