310 cases of glomerulonephritis classified morphologically according to the criteria of the WHO were analyzed retrospectively in order to determine the frequency of arterial hypertension. The overall prevalence of arterial hypertension was 61%. Hypertension was most frequent and severe in membranoproliferative and sclerotic glomerulonephritis, but often mild and transient in extracapillary glomerulonephritis. Hypertension usually developed during the early stages of the disease when kidney function was well preserved and in only 16% was hypertension first seen during the uremic stage. No correlation was found between hypertension and the presence of the nephrotic syndrome. During dialysis, hypertension was present in 78%; in 90% of these patients hypertension was "controllable" and in 10% it was "uncontrollable".