Considerable controversy exists as to whether Henoch-Schönlein purpura and Iga nephropathy are different clinical manifestations of the same disease or if, on the contrary, they are separate entities. We report on the development of Henoch-Schönlein purpura and IgA nephropathy in 2 members of the same family. Patient 1, a 63-year-old man, presented with purpura in the legs, abdominal pain, hematuria, renal failure and proteinuria. A biopsy of a purpuric skin lesion showed small-vessel vasculitis, and a renal biopsy showed diffuse proliferative glomerulonephritis with prominent IgA deposits, thus making the diagnosis of Henoch-Schönlein purpura. Serum IgA was increased. Patient 2, the 30-year-old son of patient 1, underwent renal biopsy for the investigation of microscopic hematuria and proteinuria. There was no history of skin rash, and serum creatinine was normal. A renal biopsy showed expansion of the mesangial matrix and marked IgA deposition. HLA typing confirmed that they shared a haplotype. HLA B35 or DR4 were absent. These results demonstrate that Henoch-Schönlein purpura and IgA nephropathy can possibly be genetically related and therefore support the notion that these two diseases probably share a common pathogenesis.