Using data from the Fragile Families and Child Wellbeing Study, we examine how the birth outcomes of multiracial infants differ from those of their mono-racial counterparts and the extent to which disparities in birth outcomes are due to variation in socioeconomic background, prenatal health behaviors, and availability of social support. We find that (1) the birth outcomes of multiracial infants typically fall somewhere in between those of their mono-racial counterparts, (2) outcomes vary by mother's race/ethnicity for some multiracial combinations, and (3) socioeconomic disparities account for a significant portion of the difference in rates of low birthweight between multi-and mono-racial infants born to White parents, while masking differences between infants born to Hispanic parents. Finally, differences in prenatal health behaviors and social support from baby's father also play an important role in accounting for disparities in birth outcomes between multiracial infants and their mono-racial counterparts.