We compared simultaneous direct (aortic) and indirect (oscillometric) BP measurements in 19 patients admitted to a newborn intensive care unit. Two hundred six indirect measurements were obtained from an upper extremity in 14 patients, and 50 from a lower extremity in five other patients. A regression analysis of paired data over a wide range of BPs showed excellent correlation between measurements obtained with the automated oscillometer and intra-arterial catheters. The oscillometric BP correlated equally well in both upper and lower extremities. Simultaneous upper- and lower-extremity BP measurements were taken in seven infants with low birth weights during the first 12 days of life and in ten normal term 2-to 5-day-old infants. Contrary to some previous reports, systolic, mean, and diastolic pressures were virtually identical at both sites.