Hematuria, the presence of an increased number of red blood cells in the urine, may be a sign of a serious underlying genitourinary disease. The causes of hematuria may be classified as systemic disorders, those involving the renal parenchyma (glomerular versus tubulointerstial), or those involving the urinary collecting system. The history, physical examination, and microscopic urinalysis are the key elements in reaching a dignosis. Further testing is based on these results. The primary care provider's role in hematuria evaluation involves detection, confirmation, and initiation of the evaluation process, including appropriate laboratory studies and referral as necessary. The primary care provider's prompt referral and facillitation of the hematuria evaluation is critical in achieving the best possible outcome and avoiding renal failure or the other sequelae of genitourinary disorders.