This analysis uses data from Hungary, Sweden and the United States to investigate the factors contributing to the high health risks observed among infants born within 12 months of the preceding birth. Three hypotheses for poor perinatal health are explored: confounding by prematurity, selection of high-risk mothers into short birth intervals and maternal depletion. Results show that prematurity accounts for the greatest share of the excess risks associated with closely spaced births, and for virtually all of the excess risk of late fetal death. After the confounding effects of prematurity are controlled for, the study finds that infants conceived within a few months of the preceding birth remain at higher-than-average risk of low birth weight, preterm birth and neonatal death. The results suggest that avoidance of birth intervals of less than two years could be expected to effect a 5-10 percent decreased risk of low birth weight and neonatal death.