Primary chronic glomerulonephritis is the most common cause of end-stage renal failure in Japan. The incidence in dialysis patients in Japan is about four times higher than in the United States for reason which are unclear. We conducted a nationwide survey on the natural history and treatment of primary glomerulonephritis under a program project from the Ministry of Health and Welfare of Japan entitled 'Progressive Chronic Renal Disease'. We analyzed patient characteristics, disease onset, clinical data, and histological findings in 1,850 patients with primary glomerulonephritis from 53 institutions in 1985 who underwent renal biopsy at least 5 years ago, and the follow-up study was carried out 8 years after registration. The incidence of diffuse-mesangial proliferative glomerulonephritis is 41.9%, that of minor glomerular abnormalities 17.5%, and that of focal-mesangial proliferative glomerulonephritis 13.0%. Of 1,045 biopsy specimens that were examined by immunofluorescence microscopy, 47.4% showed IgA nephropathy. Half of all cases with primary chronic glomerulonephritis were asymptomatic and were detected on routine health examination. The survival rates at 20 years from the apparent onset or earliest known renal abnormality are: focal glomerular sclerosis 49%, membranoproliferative glomerulonephritis 58%, diffuse-mesangial proliferative glomerulonephritis 66%, focal-proliferative glomerulonephritis 81%, membranous nephropathy 82%, minor glomerular abnormalities 94%, and IgA nephropathy 61%. In conclusion, a high incidence of IgA nephropathy and a better renal survival of membranous nephropathy are the features of primary chronic glomerulonephritis in Japan. This high incidence of IgA nephropathy together with its poor prognosis is probably the reason for the increased incidence of primary chronic glomerulonephritis in dialysis patients in Japan. In addition, the importance of routine health examination including urinalysis is demonstrated.