We investigated how family characteristics and experiences during early adolescence predicted timing of sexual initiation. In addition, we investigated adolescent sex and race/ethnicity as potential moderating factors. As part of the Children of the National Longitudinal Survey of Youth-1979 (CNLSY-79), 799 adolescents aged 12 to 15 years provided data at 2-year intervals between 1994 and 2010 (51.7% male; 24.5% Hispanic, 36.5% African American, 38.9% European American); their mothers also provided data in 1986 and 1994. Analyses indicated that early sexual initiation was primarily attributable to male sex, Black race, early maternal childbearing, father absence, and adolescents’ autonomous decision making during early adolescence. Multigroup path models suggested that few effects were moderated by sex or race/ethnicity. We discuss implications of these findings for future research and prevention/intervention efforts.