Compared with term infants, little information is available about the usefulness of the umbilical artery pH in relation to outcome in extremely preterm infants. This prospective study evaluates the relation between umbilical artery pH (UapH), Apgar scores, perinatal events, and outcome in infants born at less than 32 weeks' gestation. Six hundred and twenty three infants of < 32 weeks' gestation were studied. The median UapH was 7.25, with a range of 6.78-7.49. A low UapH was significantly associated with male sex, hyaline membrane disease, grade 3 or 4 intraventricular haemorrhage, and neonatal death. It was also associated with lower birth weight and lower birthweight centile. The relations between the UapH and outcomes of neonatal death, cerebral palsy, and developmental quotient at 1 year, and other perinatal risk factors were then examined using multiple logistic regression. After adjusting for other risk factors, UapH was not significantly associated with any outcome. In contrast, a low one minute Apgar (< 4) remained a significant risk factor, with odds ratios of 2.7 (95% confidence interval (CI) 1.5 to 5.2) for neonatal death and 3.8 (95% CI 1.4 to 10.4) for cerebral palsy.