Asymptomatic, atraumatic hematuria is a worrisome clinical sign for a patient that usually prompts a visit to a urologist. Hematuria is classified as microscopic versus gross; the evaluation for gross hematuria differs from that for microscopic hematuria, and the most important differentiating factor is the patient's age. The major causes of hematuria differ between children and adults, and the evaluation should reflect this. Renal disease is more common in children and malignancy more common in adults. The application and utility of laboratory tests, radiological studies, and cystoscopy are well established in adults but are more variable in children. Follow-up of hematuria after a negative evaluation is becoming more limited in adults but should be routine for children.