Between January 1, 1976 and December 31, 1987, a histological diagnosis of primary glomerular disease was made in 420 patients born and living at the time of diagnosis in a region of France with some 400,000 inhabitants. The prevalence of glomerular disease during that span of time was 1 in 1,000. The annual incidence of the disease was evaluated separately for 3 consecutive 4-year periods: period A (1976-79), period B (1980-83) and period C (1984-87). Within each of these 3 periods the number of patients with primary glomerular disease was 138, 148 and 115 respectively, and the figures for annual incidence were 8.6, 9.2 and 7.2 respectively in 100,000. Idiopathic IgA glomerulonephritis was the most common of primary glomerular diseases (34.2 per cent), and its annual incidence remained the same throughout the 3 periods: 2.6, 3.2 and 2.8 in 100,000. The incidence of membranoproliferative glomerulonephritis (7 per cent) decreased from 1980 onward (1.2, 0.5 and 0.3 in 100,000) while that of idiopathic proliferative glomerulonephritis (GNPI) with crescents slightly increased (0.25, 0.7 and 0.5 in 100,000). Acute streptococcal glomerulonephritis virtually disappeared during periods B and C. Lipoid nephrosis was significantly less frequent in period C, whereas secondary membranous glomerulonephritis progressed. There was no significant difference between the 3 periods as regards the incidence of other primary glomerular diseases. All histological types of the primary diseases became more frequent in elderly people. Thus, the overall frequency of primary glomerular diseases decreased slightly during the last 4 years, but it increased in the population aged over 65 and diminished in the younger population.