Data gathered over the course of a 20-year longitudinal study of 533 New Zealand women were used to (a) describe the extent and timing of pregnancies within the cohort up to age 20, and (b) examine the extent to which the risk of an early pregnancy was related to a range of social background, family, individual, and peer relationship factors measured over the course of childhood and adolescence. Results showed that by age 20, nearly a quarter of the sample had been pregnant at least once, with the majority of first pregnancies occurring between the ages of 17 and 20 years. The profile of those at greatest risk of a teenage pregnancy (<20 years) was that of an early-maturing girl with conduct problems who had been reared in a family environment characterized by parental instability and maternal role models of young single motherhood. As young adolescents, these girls were characterized by high rates of sexual risk-taking and deviant peer involvement. Exposure to social and individual adversity during both childhood and adolescence made independent contributions to an individual's risk of an early pregnancy. These findings were most consistent with a life course developmental model of the etiology of teenage pregnancy. Implications for teenage pregnancy prevention are discussed.