Data from a clinic sample of pregnant adolescents are analyzed for differences in fertility related variables between Mexican American and non-Mexican. The independent variables are birthplace, ethnicity, and exposure to U.S. culture of Mexican and non-Mexican adolescents. The dependent variables are talking about sex, pregnancy, birth control, hearing about birth control, and use of birth control. The data support the hypothesis that in the process of acculturation the fertility related behavior of immigrant Mexican adolescent females is affected by the indigenous United States Mexican culture rather than by United States Anglo culture. Implications for delivery of services are discussed.