We investigated the outcome of 60 infants with birth weight 501 to 750 gm, admitted to our neonatal intensive care unit over six years. Twenty-five infants were inborn and 35 outborn. Twenty-eight survived 28 days or longer (47%), and 24 were discharged (40%). The infants who died had a significantly increased incidence of intracranial hemorrhage, and their mothers had a significantly decreased use of tocolytic drugs and betamethasone. Of the 24 survivors, two died after discharge, leaving 22 long-term survivors. Of these, 18 (82%) were observed until 20 months to 7 years of age. Mean height and weight were near the fifth percentile until 3 years of age, then increased to the tenth to fiftieth percentiles between 4 and 6 years. Mean head circumferences always remained between the tenth and fiftieth percentiles. Mean IQ was 100.0 +/- 17.9 for the inborn and 87.2 +/- 15.1 for the outborn infants (excluding two whose IQ was less than 50). Two infants (11%) had neurologic sequelae, 12 (67%) were completely normal, and four (22%) were functional and of borderline or below average intelligence. No statistical differences were found between the inborn and outborn children. This study indicates that, with aggressive therapy, outcome of the infant with birth weight 501 to 750 gm is much improved.