We use administrative data on a sample of births between 1978 and 1985 to investigate the short-, medium-, and long-term consequences of poor infant health. Our findings offer several advances to the existing literature on the effects of early infant health on subsequent health, education, and labor force attachment. First, we use a large sample of both siblings and twins, second, we use a variety of measures of infant health, and finally, we track children through their schooling years and into the labor force. Our findings suggest that poor infant health predicts both mortality within one year, and mortality up to age 17. We also find that infant health is a strong predictor of educational and labor force outcomes. In particular, infant health is found to predict both high school completion and welfare takeup and length. (Contains 18 tables and 16 footnotes.)