The relationship of childhood personality type to the timing of first sexual intercourse was investigated through survival analysis. Participants from the Child Sample of the National Longitudinal Survey of Youth were categorized into one of the three personality types at 5 or 6 years of age: under-controlled, resilient, and over-controlled. Those categorized as under-controlled at 5 or 6 years of age were more likely than those resilient or over-controlled to have sexual intercourse before the age of 16. The extent to which three early adolescent factors—team/club membership, church attendance, and peer influence—mediate the association of childhood personality type to the timing of first sexual intercourse was also explored. The association of childhood personality to timing of first sexual intercourse was partially mediated by peer influence at 11 or 12 years of age. The findings are interpreted in light of their implications for researchers and practitioners interested in improving the health and well-being of children and adolescents.