For want of a more accurate term, I have retained that of "essential" for the type of hematuria which has not as yet been explained by any of the definitely established renal conditions causing hemorrhagic urine. The term "essential" should be limited to those cases of hematuria in which there is neither clinical evidence of renal insufficiency, visible organic change in the renal parenchyma nor any evidence of renal infection. The operative records of the Mayo clinic up to June 1, 1913, show twenty-six patients operated on for renal hematuria for which no evident cause could be found, and the clinical records show fifty-one patients not operated on in which the clinical diagnosis of essential hematuria was evident. SYMPTOMATOLOGY Sex. —Of the 77 patients, 58, or 75 per cent., were males and 19, or 25 per cent., females. The preponderance of males is noteworthy and is in keeping with that of renal infection occurring in the male.