Twelve neonates with hypertension have been followed for a mean of 5.75 years. At onset of hypertension, mean peak blood pressure was 159/99 mm Hg. Ten infants had umbilical artery catheters, 9 placed above the origin of the renal arteries. Radionuclide renal scan and/or angiography demonstrated renovascular disease, primarily renal artery thrombosis, in 11 infants. One-third of infants were asymptomatic, one-third had normal urinalyses and two-thirds had elevated peripheral plasma renin activities. Blood pressure normalized with medical therapy in all infants and remained normal when therapy was discontinued. Ten infants have normal creatinine clearances on follow-up but 5/11 have unilateral renal atrophy. Radionuclide scans have remained abnormal, even in infants without renal atrophy. In summary, neonatal renovascular hypertension is frequently secondary to renal artery thrombosis, associated with umbilical artery catheterization. Blood pressure usually normalizes with conservative medical management and remains normal off medications. Persistent abnormalities in renal size and function are common.