Patients with microscopic hematuria are generally referred for urologic investigation. We describe 30 patients with normal renal function referred to our clinic during the years 1970 through 1987 for evaluation of hematuria, usually microscopic, in whom prior urologic and radiological studies had failed to determine the cause of bleeding. Urinary sediment from the patients and first-degree relatives revealed hemoglobin and red blood cell casts; the inheritance pattern was consistent with autosomal dominant transmission. During follow-up for up to 18 years, renal function remained normal, thus confirming the diagnosis of benign familial hematuria. Immunoglobulin A nephropathy and Alport's syndrome were less common than benign familial hematuria and could be differentiated from it by history, physical examination, and routine laboratory testing. Since benign familial hematuria is a common disorder in adults with hematuria and normal renal function, urinary sediment from patients and family members should be examined before extensive urologic and radiological procedures are performed.