PURPOSE: Postinfectious acute glomerulonephritis usually needs no renal biopsy. But atypical clinical course and laboratory results indicate a need for renal biopsy. Therefore, to investigate clinicopathological characteristics of postinfectious acute glomerulonephritis, we compared clinical manifestations of biopsy group with those of non-biopsy group. METHODS: We reviewed the records of clinical and pathological data of 20 cases diagnosed by renal biopsies and compared them with 23 cases only diagnosed clinically. RESULT: Male : female ratio was 4.8 : 1 in biopsy group and 1.2 : 1 in non-biopsy group, so the male is more predominent in number in the biopsy group. Hypertension was documented in 52.2% of cases of non-biopsy group, which is significantly high compared to incidence of hypertension (20%) in the biopsy group. Laboratory data showed that serum creatinine, cholesterol, and 24- hour urine protein losses are significantly higher in the biopsy group. In the biopsy group, tentative diagnosis on admission were acute glomerulonephritis(45.0%), nephrotic syndrome(15.0%), membranoproliferative glomerulonephritis(15.0%), pyelonephritis(10.0%) and so on. Mean time from onset of symptoms to renal biopsy was 29.3+/-24.1(7-110) days. Fifty percent of the cases showed exudative phase, 25.0% exudative-proliferative phase. In three cases over 7 weeks, two showed proliferative phases and one sclerotic phase. CONCLUSION: Our cases of postinfectious acute glomerulonephritis diagnosed by renal biopsy had a male predominence, and lower incidence of hypertension They also tended to have decrease renal function and more urinary protein loss compared to clinically diagnoses ones without renal biopsy.