Between January 1st, 1976 and December 31st, 1990, histological diagnosis of primary glomerular diseases (PGD) was made in 480 patients born and living at the time of diagnosis in a region of France comprising 410,664 inhabitants, of whom 390,574 were aged from 10 to 80 years. The prevalence of PGD during a 70-year exposure to risk (10-80 years of age) was evaluated to 5.7 in 1000 (7.6 in 1000 males and 3,8 in 1000 females). The most common PGD was IgA nephropathy with a prevalence of 1.9 in 1000 (3.3 in 1000 males, 1 in 1000 females). The annual incidence of the disease was evaluated separately for 3 consecutive 5-year periods: period A (1976-80), period B (1981-85), and period C (1986-90). Within each of these 3 periods the number of patients with PGD was 179, 170 and 131 respectively, and annual incidence was 9.3, 8.8 and 6.7 in 100,000. The incidence of IgA nephropathy remained the same throughout the 3 periods: 2.6, 3.1 and 2.5 in 100,000. The incidence of membranoproliferative glomerulonephritis decreased from 1981 onward (0.9, 0.5 and 0.15/100,000). Acute streptococcal glomerulonephritis virtually disappeared during periods B and C. Lipoid nephrosis was less frequent in period C and idiopathic proliferative glomerulonephritis with crescents slightly increased (0.3, 0.3 and 0.6 in 100,000). There was no significant difference between the 3 periods regarding the incidence of other PGD. Incidence of IgA nephropathy was 3 to 4-fold higher in the adult aged from 20 to 60 years than in the elderly. In contrast, membranous nephropathy was 3 fold more frequent in the elderly than in the adult. Therefore only some histopathological forms have a different incidence according to age, but the major information furnished by this study is that the risk of occurrence of a PGD is similar in the population living in the area, whatever the age group (10-19 years: 6.4/10(5) inhabitants, 20-39: 7.1/10(5), 40-59: 8.4/10(5), 60-79: 8.4/10(5)). Finally, we confirm that the most common PGD going to end stage renal disease was IgA nephropathy, particularly under 60 years of age (0.8/10(5)). In contrast, membranous nephropathy was a less frequent cause of ESRD (0.2/10(5)).