Focal calcification is an occasional tubular abnormality seen in minimal-change nephrotic syndrome. Nephrocalcinosis was also reported in premature infants as a consequence of hypercalciuria resulting from long-term furosemide therapy. We describe 4 nephrotic children (3 minimal change, 1 diffuse proliferative glomerulonephritis) with transient hypercalciuria and intraluminal calcifications in renal histopathological specimens without radiologic evidence of renal calcification. These children were resistant to corticosteroid therapy and were receiving furosemide therapy along with albumin for management of oedema. Two of the children also had urinary infection. We were concerned that children with nephrotic syndrome are at risk for nephrocalcinosis, and urinary calcium and pH should be monitored carefully during prolonged furosemide use, especially in children with nephrotic syndrome with reduced initial responsiveness to corticosteroid therapy. HUM PATHOL 31:1363-1367. Copyright (C) 2000 by W.B. Saunders Company.