Minimum legal drinking age (MLDA) laws are known to reduce alcohol consumption among young adults. One additional benefit of higher MLDAs may be that they improve health outcomes among infants born to young mothers. We estimate the impact of MLDAs on infant health in the USA by comparing birth outcomes among 14–20 year old mothers who were exposed to different MLDAs because of when and where they gave birth. Infants born to mothers who were between the ages of 21 and 24 years are included as a control group. We find that low MLDAs are associated with very small birth weight reductions, but have a little relationship with other traditional measures of infant health. We find compelling evidence, however, that a low MLDA increases the probability of a female birth, which suggests that restricting alcohol access to young mothers may reduce fetal deaths. Copyright © 2013 John Wiley & Sons, Ltd.