The epidemiologic data concerning the value of monosymptomatic microscopic hematuria as a screening test can be summarized in four points: 1. In an unselected population the chance of diagnosing serious urologic disease is about 5% and below 1% for tumors. 2. There is no difference between the result obtained by dip-stick or microscopic evaluation of the urinary sediment. The grade and duration of the symptom does not serve to select a group at risk, nor does age. 3. It is more realistic to admit 10% of non-classified microscopic hematurias than to classify the phenomenon with an unrealistic diagnosis. A benign disease may hide a serious one. 4. It is not certain that the early discovery of renal or bladder tumors makes a significant difference to prognosis in terms of survival. A detrimental effect of delayed treatment has been proved only for microinvasive bladder cancer.