This paper attempts to explain the differences in birthweight observed between blacks, white Anglos, Chicanos, and other racial and ethnic groups. The analysis focuses on the role of income and financial assistance from relatives and public programs. Using data from the NLS Youth Panel, I construct a causal model of birthweight containing exogenous social and demographic risk factors and intervening proximate determinants of birthweight. A substantial part of the gap in birthweight between white Anglos and other ethnic groups (especially blacks) can be explained by the unfavorable socioeconomic and demographic characteristics of the latter. On the other hand, blacks and other minorities smoke less and have other favorable proximate characteristics that depress differences in birthweight. When these proximate determinants are controlled, large ethic differences in birthweight remain unexplained by income and other sociodemographic factors.