Twenty-four patients with thalassemia major and no urinary tract complaints underwent excretory urography. The kidneys were large bilaterally in 17 patients; 2 other patients had enlargement of the left kidney. The autopsies of 13 patients were reviewed; the kidneys were large in all 13. Tubular dilatation was constant, and the glomeruli were normal. Iron deposition was relatively low; extramedullary hematopoiesis, fibrosis, and scarring were insignificant in the kidneys of the patients who died of thalassemia major. Tubular dilatation, which causes an increase in renal mass, is the most likely explanation of the large kidneys in patients with thalassemia major.