The relationship of renal and central nervous system injury was prospectively evaluated in 120 asphyxiated infants. Renal evaluation findings were considered abnormal if there was oliguria (urine output less than 1 ml/kg/hr), which was designated transient if present in the first 24 hours only and persistent if present for at least 36 hours, or if the urinary beta 2-microglobulin concentration from first-void urine was elevated: (1) Thirteen infants had persistent oliguria; the urinary beta 2-microglobulin level was elevated in all. The six term infants had clinical signs consistent with hypoxic-ischemic encephalopathy (HIE); all six had ultrasonographic abnormalities. The outcome was poor (i.e., death or long-term neurologic deficits) in five of six infants. The seven preterm infants with persistent oliguria had clinical evidence of HIE, and three infants had intraventricular hemorrhage; all seven infants died. (2) Fifteen infants had transient oliguria (beta 2-microglobulin level was elevated in eight infants). Two of the eight term infants had evidence for HIE; the cranial ultrasound scan was normal in all. At follow-up, seven term infants are normal and one is abnormal. Six of the seven preterm infants with transient oliguria had clinical evidence of HIE; three infants had intraventricular hemorrhage. Three infants died, and the four survivors are normal at follow-up. (3) Ninety-two infants had normal urine output. Of the 22 term infants, two developed signs of HIE, and the ultrasound scan was abnormal in three infants. Of the 70 preterm infants, eight (11%) had clinical signs consistent with HIE, the ultrasound scan was abnormal in 20 of 64 (31%) infants scanned, and 14 (20%) infants died. Most of the followed infants are normal. Thus oliguria was significantly associated with clinical signs of HIE, including seizures, death (specifically in the premature infant), and long-term neurologic deficits. These data suggest that oliguria in the perinatal period is a sensitive indicator of infants at risk for long-term neurologic deficits.