Human immunoglobulin A is represented by two structurally and functionally distinct subclasses: IgA1 and IgA2. IgA1, which is almost exclusively present in the mesangial deposits in IgA nephropathy patients, contains in its hinge region three to five O-lined carbohydrate chains. A fraction of IgA1 molecules in the circulation of IgA nephropathy patients exhibits aberrant glycosylation. As a result of changes in glycosylation, the neoepitopes represented by glycans are exposed and recognized by naturally occurring antibodies with antiglycan specifities, and immune complexes are generated. The deposits of these immune complexes in the glomerular mesangia elicit inflammatory response known as IgA nephropathy. Epidemiological studies have shown that dominant hematuria, either isolated or combined with mild proteinuria, is the most frequent urinary syndrom in glomerulonephritis. The morphologic finding of this syndrom is most frequently IgA nephropathy. Originally considered a benign disease, IgA nephropathy is now recognized as a frequent cause of chronic renal failure. The progression is signalized by increasing proteinuria and hypertension. Therefore. a control of blood pressure and lowering of proteinuria remain the corner-stones of the treatment. Angiotensin converting enzyme inhibitors and ATI blockers may lower both blood pressure and proteinuria and are now increasingly promoted even for treatment of normotensive patients. Steroids are administered to patients with severe proteinuria. High-doses of fish oil seem to slow down the rate of renal failure.