Benign prostatic hyperplasia (BPH) is a very prevalent disease process in the aging male. It is characterized by symptoms referred to as 'prostatism'. Although it rarely threatens the life of the patient, it does affect the quality of his life; the evaluation of a patient with BPH should therefore focus on a quantitative assessment of the symptoms and the degree to which they bother the patient. The baseline evaluation of patients with BPH should also include medical history, focused physical examination, urinalysis, and assessment of renal function. Other tests, such as prostate-specific antigen measurement, residual urine measurement, uroflowmetry, pressure-flow studies, and imaging of the urinary tract, should be used after their benefits and risks have been weighed. Tests must be examined for their ability to differentiate BPH from other conditions, predict the outcome of therapy, and improve the selection process for certain treatments.