Between 1 January 1976 and 31 December 1986, primary glomerulonephritis was histologically diagnosed in 319 patients, living in a region of 675,000 inhabitants at the time of renal biopsy. The prevalence of primary glomerulopathy was 0.4/1000 inhabitants. The annual incidence was determined during two 5 year periods: period A (1976-1980) and period B (1981-1985): they were, respectively, 3.4 and 4.5 for 100,000 inhabitants. Berger's focal glomerulonephritis was the most common (30 p. 100) and its incidence was increasing. In contrast, membranoproliferative and acute glomerulonephritides were sharply decreased (almost disappeared), while membranous glomerulonephropathies and glomerulopathies with minimal glomerular lesions or proliferative forms with crescents increased. All primary glomerulonephritides were more prevalent in men and their frequencies increased with age. Our findings lead to the following conclusions: a) the low prevalence and incidence of primary glomerulopathies (3 times less than in other published studies) probably reflect the under medicalization of our region and the attractiveness of neighbouring metropolis, rather than a real decrease in the disease; b) the quasi- disappearance of acute and membranoproliferative glomerulonephropathies and the high incidence of IgA glomerulonephropathies suggest that their pathogenetic associations with infections sensitive to antibiotics are different; c) the increased frequency of membranous glomerulonephropathy and the glomerulopathy with minimal glomerular lesions in aged subjects is most likely due to their polymedication.