Eighty-two patients, 56 male and 26 female, biopsied since 1972 had IgA nephropathy. At the time of kidney biopsy, 24 patients were children and 58 were adults. In both groups the clinical course was documented in sufficient detail to allow prediction of disease outcome. Twenty-six (45%) of the adult patients had chronic renal insufficiency either at first evaluation or subsequently. Fourteen eventually required chronic hemodialysis. Hypertension as the initial sign of disease was seen more frequently in patients with chronic renal insufficiency. Adult males were more likely to have chronic renal insufficiency. The life table method was used to predict age at initiation of dialysis and kidney survival from date of onset of clinically apparent disease. Thirty-five percent of the male patients were predicted to require dialysis by age 40. Kidney death was predicted at 10 years from onset for 33% of male and 22% of all patients biopsied as adults. While all patients with progressive disease had over 2.0 g/24 h urinary protein excretion at least once, many individuals with serum creatinine concentration below 1.5 mg/dL showed marked fluctuation in degree of proteinuria, often exceeding 2.0 g/24 h. Thus, in some cases, degree of proteinuria was not a reliable predictor of outcome.