In a single year in New York City, we identified 1413 neonates who were transferred for medical care from their hospitals of birth; 83% of transferred infants were sent from Level 1 hospitals (no special facilities for sick infants) to Level 3 hospitals (newborn intensive care units). Level 2 hospitals (those with an intermediate level of care) participated little in the transfer process as either senders or receivers. Infants weighing more than 2250 g were rarely transferred. Among low-birth-weight infants born at Level 1 hospitals, the major determinants of transfer were birth weight, gestational age, and Apgar score. Peak transfer rates were for infants weighing 1000-1750 g (84% transferred), those with gestational ages of 28-31 weeks (79% transferred), and those with Apgar scores of 4-6 (68% transferred). Infants with values either above or below these modes were transferred less frequently. Transfer from Level 2 hospitals was also significantly related to birth weight and Apgar score. Socioeconomic indicators such as race, maternal education, ward/private status, and financial coverage for the delivery had no effect on transfer rates. Transferred low-birth-weight infants were a highly selected sample of low-birth-weight infants. Infants transferred from Level 1 hospitals were those in better condition (higher Apgar scores) when weighing less than 1750 g, and those in worse condition (lower Apgar scores) when weighing more than 1750 g.