The frequency of mesangial IgA deposition was examined in 250 consecutive autopsy cases without known renal disease. Diffuse granular mesangial deposits of IgA were detected in 12 of 250 cases (4.8%). In six patients IgA deposits were associated with liver cirrhosis. Six patients (2.4%) suffered from various other conditions including endocarditis, bronchial asthma, cardiovascular disease, and neoplasia. Two of these patients had completely negative urine analysis on repeated investigations, whereas three patients exhibited microscopic haematuria and/or mild proteinuria. IgA₁ was the major constituent in all specimens. C3c deposits in glomeruli were detected in one kidney. Our findings indicate that clinically overt renal disease is present in only a limited proportion of individuals with mesangial IgA deposits. Apparently, it represents the tip of an iceberg.