Seven children with asymptomatic gross hematuria are described. Six had recurrent hematuria; one had a single episode. Occasional global glomerulosclerosis and/or mesangial electron dense deposits were present in the three patients in whom renal biopsy was performed; the changes were felt to be insufficient to account for the hematuria. None of the patients had urolithiasis or any significant urinary tract abnormality. One was an adopted child; a family history of urolithiasis was obtained in the other six. Idiopathic hypercalciuria was documented in six patients; the seventh subsequently passed a calcium oxalate calculus. One patient is 10 weeks of age at the time of this submission. Of the remainder, three patients received no specific therapy; renal calculi developed six months, six years, and eight years later. Three patients were treated with a thiazide diuretic soon after onset of hematuria and confirmation of idiopathic hypercalciuria; there was complete cessation of hematuria within five days with no recurrence as long as therapy was continued. We suggested that measurement of urinary calcium excretion as part of the initial evaluation of a child with gross hematuria may, in some cases, obviate invasive investigations and allow for effective therapy.