Idiopathic mesangial IgA nephritis (Berger's disease) and Schönlein-Henoch purpura mesangial IgA nephritis (SHP) have a common immunopathological pattern. There is a weak association with the MHC class I antigen, B35, which is a poor prognosis marker in Berger's disease and which predisposes to renal involvement in SHP. There is also an association with the MHC class II antigen, DR4, whose signification remains unclear. Many familial cases of Berger's disease have been reported in patients bearing the HLA-B35 antigen. We proposed that Berger's disease and SHP should be viewed as a unique entity according to their common immunogenetics and also common immunopathology.