Although its prevalence and clinical importance in the United States are stated to be low, we believe IgA nephropathy occurs as commonly in this country as in Western Europe. Initial reports suggested the disease was perhaps restricted to France and synonymous with "benign recurrent hematuria," but longer follow-up has proven both conclusions incorrect. Obviously, major gaps persist in our understanding of the immunopathogenesis and the natural history. The latency of the American investigative response calls for more intensive clinical and laboratory studies of the most common primary glomerulonephritis worldwide.