Quantitative and semi-quantitative morphological analysis of 41 cases of idiopathic membranous glomerulonephritis revealed glomerular hypercellularity in 24 cases and abnormal parietal epithelium in 25 cases. Abnormal parietal epithelium included crescents and prominent parietal epithelium (at least ten enlarged cells with round or ovoid nuclei lining Bowman’s capsule of two or more glomeruli per biopsy). The clinical course (mean follow-up = 5.1 years) was correlated with biopsy findings. 8 of 17 patients with normocellular glomeruli, but only 3 of 24 patients with hypercellular glomeruli achieved complete clinical remission. 10 of 16 patients with normal parietal epithelium, but only 1 of 25 patients with abnormal parietal epithelium achieved complete remission. Of 9 uremic patients, all but 1 had abnormal parietal epithelium in their biopsies. Glomerular cellularity and parietal epithelium may be useful prognostic indices in idiopathic membranous glomerulonephriti