Finasteride is a novel therapeutic agent that selectively inhibits the enzyme 5 alpha-reductase, thereby reducing prostatic dihydrotestosterone (DHT) levels and prostate size. In men with symptomatic benign prostatic hyperplasia (BPH), these effects have been associated with improvements in peak urinary flow rate and urological symptoms; withdrawal from therapy, however, results in regrowth of the adenoma and long term therapy is therefore necessary. Although the magnitude of clinical improvement seen with finasteride has been perceived to be modest [especially when compared with that associated with transurethral resection of the prostate (TURP)], it has been maintained in the medium term (up to 2 years) and thus may represent significant reversal of disease progression. Such beneficial effects, however, may not become apparent until completion of at least 6 months of therapy. Furthermore, since clinical studies have been unable to proactively identify a responsive subgroup, a trial period of 6 or possibly 12 months is necessary to assess patient responsiveness. Despite these potential shortcomings, the benefits of therapy appear to outweigh the risks. Indeed, finasteride is well tolerated; most adverse events have been related to sexual dysfunction (decreased libido, ejaculation disorders and impotence) and occurred in only a small proportion (about 2 to 3%) of patients. Moreover, although there has been concern that finasteride might mask the detection of prostate cancer through its decremental effects on serum prostate specific antigen (PSA) levels, careful monitoring in clinical trials appears to have avoided this problem. Thorough pretreatment assessment and periodic follow-up examinations for malignancy are therefore required in clinical practice. The role of finasteride in the treatment of patients with BPH is still emerging and will no doubt gain in clarity with further planned investigations. TURP (or other invasive procedures such as the insertion of prostatic stents in patients unsuitable for resection), continues to be the mainstay of therapy for those patients with severe symptomatic BPH. However, available data support a first line role for finasteride in the treatment of patients with uncomplicated symptomatic BPH. Within this setting, finasteride appears to offer a needed additional treatment option for those patients in whom surgery is not indicated, and may be of special benefit to the considerable proportion of patients who opt not to undergo prostatectomy.