ObjectiveTo examine the risk factors for adult (aged 20 years and older) paternity in births to teenagers (14-17 years of age).MethodsThis was a population-based, retrospective cohort analysis of 27,215 adolescent mothers residing in California who had a live singleton birth during 1993. Adjusted risks for adult paternity by paternal and maternal characteristics were derived from comparisons of adult-teen and teen-teen couples.ResultsAdult fathers, who were responsible for 49.2% of births to teenage mothers, were a mean of 6.4 years older than the mother. The most important risk factors for adult paternity were as follows: father's (odds ratio [OR] 5.19;95% confidence interval [CI] 4.43, 6.08) or mother's (OR 1.33; 95% CI 1.14,1.55) educational attainment of at least 3 years lower then expected for their age, two or more previous live births (OR 3.34; 95% CI 2.48, 4.53), mother's birthplace outside the United States (OR 2.33; 95% CI 2.11, 2.58), father's (OR 2.16; 95% CI 1.98, 2.36) or mother's (OR 1.28; 95% CI 1.15, 1.42) educational attainment 1–2 years lower than expected for their age, one previous live birth (OR 1.92; 95% CI 1.75, 2.12), and Asian (OR 1.29; 95% CI 1.04, 1.62) or African American race (OR 1.25; 95% CI 1.06, 1.46) of the father.ConclusionsTeenage pregnancy prevention programs must address adult paternity, which contributed to almost half of the births in out study. These programs should consider education adequacy, cultural beliefs and practices, previous live births, and race and ethnicity when designing programs to decrease the number of adults involved in teenage births.