GROSS HEMATURIA in a child is both unusual and alarming. In a previously healthy child without a history of trauma, the differential diagnosis in these cases includes glomerulonephritis, tumors of the urogenital system, hematologic diseases, inflammatory conditions, and reticuloendothelial diseases. Rarely is hydronephrosis considered a cause of gross hematuria. We recently saw an 8-year-old boy who had sudden onset of gross painless hematuria with the passage of clots. The anomaly and the hydronephrosis coexisting and the satisfactory surgical results were unusual enough to be reported. Report of a Case An 8-year-old boy was admitted to the hospital on April 8, 1966, because of painless gross hematuria of 12 hours' duration. At the onset of the hematuria, a few clots were present in the voided specimens. These were passed after fleeting and colicky pains in the right flank. The boy's past health had been good and there had been no previous