Glomerulonephritis with mesangial deposition of IgA was diagnosed in 31 patients. In Spain this disease is the second more frequent primary glomerulonephritis, representing 27% of them. One out of every four patients with IgA mesangial glomerulonephritis ends the clinical course in renal failure. Such bad evolution might be predicted by the existence of arterial hypertension, severe proteinuria, degree of glomerular sclerosis, presence of HLA Bw35, and increased polymeric IgA in serum. The present pathogenetic concepts are reviewed.