Urinary calcium excretion was assessed in 83 consecutive children with gross or microscopic hematuria in whom the presence of proteinuria or urinary-tract infection had been excluded. Twenty-three children had hypercalciuria. Clinical features that were more commonly associated with hypercalciuria included gross hematuria and a family history of urolithiasis. No clinical or pathological basis for the hematuria was determined in 22 of the 23 children with hypercalciuria or in 38 of the 60 children with normal calcium excretion. Urolithiasis developed in two children with hypercalciuria during the period of study. Oral calcium-loading tests were performed in all 23 children with hypercalciuria. Absorptive hypercalciuria was demonstrated in 10 children, whereas 13 had renal (fasting) hypercalciuria. Hematuria resolved during anticalciuric therapy in 20 of the 23 patients with hypercalciuria. We conclude that determination of urinary calcium excretion is warranted in the routine evaluation of children with hematuria.