In this study incidence rates of idiopathic glomerular disease in 1.5 X 10(6) Dutch adults between 16 and 65 years of age were determined, as well as the prevalence of these diseases in terms of indication for renal biopsy. The study was conducted between 1978 and 1985; indications for renal biopsy in decreasing hierarchical order were recently discovered uremia, nephrotic syndrome, chronic hematuria of less than two years duration with or without proteinuria or disturbed renal function, and chronic proteinuria of less than two years duration, of unknown origin. The main findings are fourfold. The incidence of IgA nephropathy and thin glomerular basal membrane lesions was high, 19 and 13 per 10(6) adults respectively, and the prevalence in patients biopsied because of non-azotemic chronic hematuria was 31% and 22%, respectively. In the normotensive non-azotemic adults biopsied because of chronic, mild proteinuria the prevalence of focal segmental glomerular sclerosis and vascular hyalinosis was both 41%. Of the patients biopsied because of nephrotic syndrome the prevalence of membranoproliferative glomerulonephritis (5%) was low, as was the incidence (less than 2 per 10(6) adults per year). Finally, the prevalence of diffuse sclerosing glomerulonephritis was 25% in patients biopsied because of uremia. This study is useful for the differential diagnosis of idiopathic glomerular disease.