One of the most difficult ethical issues in neonatal intensive care concerns the treatment of extremely low birth weight infants (ELBW). Because of their extreme prematurity, aggressive medical intervention is needed to sustain life. Advances in perinatal medicine have made it possible for these extremely immature infants to survive. More importantly, although the mortality and long-term morbidity are high, particularly for infants less than 700 gm, many of the survivors are expected to become productive members of society and produce measurable economic benefit. The limits set for aggressive management of the VLBW infant have gradually been lowered in virtue of the successful survival at each birth weight. It appears that, with each reduction in the birth weight at which maximal efforts should be used, enough babies have survived to encourage us to continue. As we drive to bring the limit of viability to lower gestations and lower birth weights, we are finding some biologic limitations to extrauterine survival that present technology and knowledge cannot overcome. Unquestionably, there is a need for more comprehensive statistics to allow us to define the lower limit of survival. Because of the poor survival rate among infants weighing less than 700 gm, and because of the high cost of their care and statistically poor quality of life among many of the surviving infants, it has been suggested that perhaps a less aggressive approach should be adopted for those extremely immature infants. However, some recent data indicate that aggressive treatment is effective in saving lives, even at the lower spectrum of birth weight, and many of the survivors are normal or have mild handicaps. The importance of economic considerations to solve the ethical dilemma posed by the intensive care of ELBW infants is being questioned. Concerns that reflect moral absolutes cannot be adequately answered in terms of mere dollars and cents. Although the cost of neonatal intensive care is high on a per diem or per case basis, it appears to be reasonable in relation to the health benefits it provides. For infants in the weight class less than 750 gm, probably none would have survived in the absence of neonatal intensive care. We believe that a policy of benign neglect for the ELBW infant is not justified in the present era of perinatal medicine. Given these considerations, we think that aggressive treatment is reasonable, at least initially at birth.(ABSTRACT TRUNCATED AT 400 WORDS)