Cost-benefit analysis was performed on the care of 247 infants weighing between 500 and 999 g at birth, admitted to Women and Infants Hospital of Rhode Island between January 1977 and December 1981. The neonatal mortality was 68%. Eighty-seven percent of the survivors were evaluated neurodevelopmentally for 1 to 5 years: 74% were normal or minimally impaired, 10% were moderately impaired, and 16% were severely handicapped. Using these data in conjunction with cost information obtained from the hospital and therapeutic care facilities for handicapped children, total lifetime costs for the care of these infants were estimated. In 1982 dollars, present values of costs ranged from $362,992 per survivor for those weighing between 600 and 699 g to $40,647 per survivor for those weighing between 900 and 999 g, resulting in an inverse correlation between cost per survivor and birth weight (P less than .001). We estimated present values of expected lifetime earnings per survivor, with a range of zero earnings for infants between 500 and 699 g, to $77,084 for those with birth weight of 900 to 999 g. It is concluded that from the standpoint of cost-benefit analysis as was used for this study population, neonatal intensive care may not be justifiable for infants weighing less than 900 g at birth.