The purpose of this study was to determine whether pregnant Mexican-American teenagers who are acculturated to American lifestyles have different medical and psychosocial problems from those who are more recent immigrants. Consecutive pregnant Mexican-American (or Mexican) teenagers attending a university obstetrics clinic for teenagers were divided into two groups based on country of birth of parents and teen, citizenship, preferred language, and years of U.S. residence. There were 60 in the acculturated group (G1) and 56 in the recent immigrant group (G2). Acculturated teenagers were younger at first sexual intercourse, completed more years of schooling, and sought earlier prenatal care (p < 0.05 for all above). Both groups delivered full-term singletons of average birth weight (mean = 3337 g +/- 477 g). All G2 fathers were Mexican, older (p < 0.05), more likely to be married to G2 teens (p < 0.001), and employed (p < 0.01). The G1 fathers completed more years of schooling (p < 0.05), and 10% were non-Mexican. These data underscore the need to consider acculturation, as well as ethnicity in understanding the experience of pregnant teenagers.