Symptomatic neonatal hypertension, defined as a mean arterial blood pressure (MAP) greater than 70 mm Hg for 3 separate determinations, was observed in 2% of all admissions (20 of 988) to the intensive and intermediate care nurseries. Evidence of renal dysfunction occurred in 85% of these infants, including increased plasma renin, abnormal renal scintiscans, and pathologic evidence of renal vascular embolism or thrombus in 13 of 20. Cardiac complications were present in 55% of affected patients, and features of hypertensive retinopathy were noted in 53% of those examined. Medical management during the neonatal period successfully controlled hypertension in all infants. Higher than usual doses of three or more antihypertensive medications were necessary in 15 of 18 treated patients. The infants requiring these high doses did not develop adverse side effects. In light of the fact that 80% of our affected patients had indwelling umbilical arterial catheters whose tips were in the thoracic aorta, the possible role of catheter management, position, or placement in the pathogenesis of this disorder is suggested.