Few data are available on the prenatal health problems and postnatal outcomes of Mexican-American pregnant teenagers. Our study population consisted of 199 consecutive Caucasian, Mexican-American, or Black pregnant adolescents, ages 11-19 years, followed prospectively at the University of California San Diego Medical Center Teen Obstetric Clinic from 1978 to 1981. The patients included 79 Caucasians, 76 Mexican-Americans, and 44 Blacks. Mexican-American adolescents were shorter, less likely to be cigarette smokers, and delivered heavier babies than their non-Hispanic peers. More than 50% of the teenagers in all three groups gained more than the recommended upper limit of 12 kg during the pregnancy, but excessive gain was most pronounced in the Mexican-American group. Black pregnant adolescents were more likely to be anemic and had a higher frequency of goiter. It is recommended that data concerning Hispanic mothers and infants be analyzed separately from data of Caucasian and Black adolescents to more accurately define their pregnancy problems.