Obstetric decisions regarding premature (23 to 32 weeks' gestation) infants must be based on gestational age. However, most reports of the survival of premature infants are based on birth weight. The present report relates the perinatal survival and morbidity of 105 newborns to the obstetric gestational dating criteria between 23 and 32 weeks' gestation. Gestational age was determined from at least four obstetric criteria including the first day of the last menstrual period, early pelvic examination, the earliest auscultation of fetal heart tones with a fetoscope, fundal height measurements in centimeters between 20 and 30 weeks' gestation, and sonographic gestational age measurements. At 23 to 26 weeks' gestational age, nine (39%) of 23 neonates survived. Five of nine survivors had moderate to severe intracranial hemorrhage, three had moderate to severe bronchopulmonary dysplasia, and three had moderate to severe retrolental fibroplasia. At 27 to 29 weeks' gestational age, 25 (93%) of 27 neonates survived. Of the 25 survivors, three had moderate to severe intracranial hemorrhage, one had moderate to severe bronchopulmonary dysplasia, and one had severe retrolental fibroplasia. At 30 to 32 weeks' gestational age, 52 (95%) of 55 neonates survived. Three of the 52 (6%) survivors had serious neonatal morbidity consisting of moderate to severe intracranial hemorrhage (three neonates) and moderate to severe bronchopulmonary dysplasia (one neonate). Thus, ten of 34 (29%) survivors between gestational ages of 24 to 29 weeks had a serious morbidity versus only three of 52 (6%) survivors between 30 to 32 weeks' gestation (P less than .01).