To minimize the selection bias inherent in reporting results gathered only in neonatal intensive care units, this study presents survival and respiratory course data on all 299 infants of birthweight 501 to 1500 gm liveborn to residents of the North Central Illinois Perinatal Region in 1985-1986. The survival rate was 86.8% (171 of 197) for infants between 1001 and 1500 gm, but only 35.3% (36 of 102) for infants weighing less than 1001 gm. In all, 207 infants (69.2%) survived. One hundred eighty-six infants (62.2%) required mechanical ventilation, and 122 (65.6%) ventilated infants survived. Seventy-five (40.3%) ventilated infants developed lung rupture and 54 (29%) developed chronic lung disease (CLD), as manifest by a supplemental oxygen requirement at 28 days of age. Lung rupture significantly predicted death in the first 7 days, the development of CLD, and fatal CLD. These data portray an accurate picture of the survival and ventilatory course of this group of babies because every member of the entire regional cohort is included.