The authors present an evaluation of the role of acculturation in smoking practices and pregnancy outcome (N = 767 births) in a national sample of Mexican American women. Data employed are from the 1982-1984 Hispanic Health and Nutrition Examination Survey. The prevalence rates of smoking during pregnancy, low birth weight (< or = 2500 g), and preterm delivery (> or = 3 weeks prior to the expected date) are higher among more acculturated women compared with less acculturated women. Among the more acculturated women, the prevalence of smoking and poor birth outcomes did not increase linearly with increasing American orientation. Rather, women in the third quartile of acculturation scores, i.e., those with a moderate American orientation, experienced significantly poorer birth outcomes than women with either a stronger American orientation or a Mexican orientation. Women at this moderate level of acculturation appear to have the greatest need for public health services rather than women with the lowest level of acculturation (non-English speaking, lowest income) as a means of improving their pregnancy outcomes.