The following conelusions can be drawn from this study of the clinical and morphological features of perimembranous glomerulonephritis (PGN) in 100 patients and in 31 patients who had serial renal biopsies: (1) PGN appears in every age group and is especially frequent between 31–40 and 51–60 years; it occurs more often in males than in females; (2) PGN begins in most cases idiopathically without preceding diseases; (3) the predominant early symptoms of PGN are edema and/or proteinuria; (4) the nephrotic syndrome is the most striking symptom when PGN is fully developed; (5) Hypertension is frequently observed in patients with PGN; the combination of the nephrotic syndrome and hypertension is observed more frequently than the nephrotic syndrome and normal blood pressure; the combination of hypertension, hematuria and the nephrotic syndrome is also frequently observed; (6) proteinuria is most marked in the early stages of PGN and decreases as the transformations of the glomerular basement membrane progress; (7) PGN is a proliferative glomerular disease, but the proliferation is mild and may only be a proliferation of the mesangial cells; (8) the prognosis of PGN is unfavorable; clinical improvement can occur without an improvement in the morphological features of the glomerular basement membrane.