The prevalence of hypertension in 288 patients with primary chronic glomerulonephritis was compared with that observed in a control group of 3,477 subjects from the same geographic area. 23.3% of the patients and 12.8% of the general population were hypertensive (p less than 0.01). However, if only patients with normal renal function were considered, prevalence of hypertension (12.7%) was not higher than in the control group. Hypertension was more frequent in focal segmental sclerosis (30%) and in membranous glomerulonephritis (26%) than in IgA nephropathy (9%), membranoproliferative glomerulonephritis (11%) and IgM mesangial glomerulonephritis (12%). Five years after renal biopsy, 92% of normotensive and 47% of hypertensive patients remained with normal renal function (p less than 0.001). These findings suggest that the high prevalence of hypertension in chronic glomerulonephritis is related to the declining renal function. On the other hand, hypertension appears to represent a bad prognostic sign.