We compared the age-adjusted birth prevalence of Down syndrome at birth among several racial/ethnic groups in the United States using birth data for the years 1989 to 1991 in the United States (N = 10, 229, 500). Logistic regression models which included variables controlling for maternal age and race/ethnicity as well as separate (stratified) logistic models for African Americans, Mexicans and Non-Hispanic Whites were estimated to determine whether the effect of maternal age on the risk for Down syndrome was similar for African Americans, Mexicans and Non-Hispanic Whites. Results of logistic models showed that the age-adjusted birth prevalence of Down syndrome was 35% lower in African American [Adjusted Odds Ratio (OR): 0.65, 95% C.I., 0.60 - 0.71], and 11% lower in Mexican [Adjusted OR: 0.89, 95% C.I., 0.81 - 0.98] as compared with Non-Hispanic White infants. On the other hand, the birth prevalence of Down syndrome among Puerto Rican infants [Adjusted OR: 0.97, 95% C.I., 0.73 - 1.28] was similar to that of Non-Hispanic Whites. Results of the separate logistic models for the effects of maternal age on the risk for Down syndrome in African Americans, Mexicans and Non-Hispanic Whites further suggested that the relationship between maternal age and risk for Down syndrome may differ among races with a curvilinear relationship among African Americans and Mexicans in contrast with a monotonic increase in risk with increasing maternal age among Non-Hispanic Whites. The stratified models also suggested that infants of Mexican and Non-Hispanic White mothers who were ≥ 30 years of age had significantly higher risks for Down syndrome whereas for African Americans, the risk was only significant for ≥ 35 years of age. Conclusions: 1. Infants born to African American mothers have a 35% lower maternal age-adjusted risk of Down syndrome as compared with Non-Hispanic White infants. 2. The relationship between maternal age and the risk for Down syndrome may differ among races with a curvilinear relationship among African Americans and Mexicans as compared with a monotonic increase in risk with increasing maternal age among Non-Hispanic Whites.