A retrospective analysis of 565 cases of IgA nephropathy, defined by the presence of predominant and diffuse IgA deposits in the glomerular mesangium, led to the classification of 510 primary forms or Berger's focal glomerulonephritis and 55 cases secondary to Henoch-Schönlein syndrome. Crescent proliferation was observed in 9.4% of the renal biopsies taken from patients with Berger's disease; they were generally contained and do not seem to be correlated with disease prognosis. On the other hand, the presence of glomerular crescents seems to represent a major prognostic factor in Henoch-Schönlein purpura-associated glomerulonephritis, because all the patients who developed chronic renal failure (5%) had extracapillary proliferation affecting more than 25% of the glomeruli. The detection of glomerular crescents in Henoch-Schönlein syndrome justifies the initiation of aggressive therapy.