The natural history of benign prostatic hyperplasia (BPH) involves two phases. The first, or pathologic phase, is composed of two stages, microscopic and macroscopic, neither of which produces symptomatic clinical dysuria. Nearly all men throughout the world eventually develop microscopic BPH if they live long enough. In only about 50% of men, however, does microscopic BPH grow to produce a macroscopic enlargement of the gland, suggesting that additional factors are required for BPH progression. The second, or clinical, phase of BPH involves the progression of pathologic BPH to its clinical form, in which the patient develops symptomatic dysuria. Again, only about one half of the men with macroscopic BPH progress to clinical BPH. Although macroscopic enlargement of the prostate is necessary for the development of clinical BPH, it is usually not sufficient by itself for the progression to clinical BPH. Additional factors are required (e.g., prostatitis, vascular infarct, tensile strength of the glandular capsule). Successful treatment does not, therefore, require the prevention of pathologic BPH; instead, what is needed is a therapy to prevent or reverse the progression to clinical disease.