In this analysis of 43 patients with IgA nephropathy, renal morphology was correlated with clinical data. Gross hematuria and mild proteinuria were typical among younger patients. Among older individuals the clinical spectrum was wider. A comparison with data previously obtained from the normal population indicated that disease-related glomerular sclerosis was present in 1/3 of initial biopsy specimens. The prevalent pattern of glomerular sclerosis was that of global tuft collapse, the type of sclerosis known to result from ischemia. Intrarenal vascular sclerosis was present in 1/3 of initial biopsies. Follow-up specimens from 6 patients showed progression of glomerular sclerosis, vascular sclerosis or both. Hypertension occurred in over 1/4 of patients. It is proposed that progressive renal damage in IgA nephropathy may not be solely immunologically mediated. Glomerular sclerosis may also be mediated by vascular sclerosis, or alterations in intrarenal hemodynamics in glomerulonephritis may have a direct damaging effect on both the glomerulus and the intrarenal vasculature.