BACKGROUND Benign prostatic hyperplasia (BPH) is one of the most common urinary disorders in elderly men. The symptoms of this disease are increased prostate size, bladder outlet obstruction and lower urinary tract disorders. It influences bladder infections, bladder stone formation and increases the risk of urinary retention which can cause renal failure. It is necessary for the disease to be treated operatively. The number of conducted surgical interventions for pharmacotherapy has been significantly reduced in recent years due to increased efficacy in conservative therapy including combined treatment mostly with two groups of drugs: finasteride and alpha-blockers with different pharmacological activities. The aim of the study was to evaluate finasteride efficacy in the treatment of benign prostatic hyperplasia. METHODS The clinical trial was conducted from October 2008 to November 2009. According to the urologist's recommendation the patients took finasteride at a dose of 5 mg daily. A total of 4,315 patients participated in the clinical trial and were enrolled in 50 urological centres in Poland. The average age of the patients was 66.5 years, the youngest patient was 46 and the oldest was 91 (median 67.00 years, standard deviation SD±8.101). The use of finasteride at least for 2 weeks was the criterion for the patient to be included in the study. The medical trial lasted 12 months and consisted of 6 visits at which data relating to IPSS, QoL, intensification of urinary system symptoms, the results of the additional studies, PSA serum concentrations, the urinary tract USG with evaluation of residual urine and prostate, urine analysis with evaluation of crystalline, uroflowmetry, transrectal ultrasonography (TRUS) and biopsy were recorded. The study did not exclude the combined treatment with finasteride and alpha-adrenergic blocking drugs. RESULTS Prostatocystitis was diagnosed in 30 men among the patients treated at the first visit after the digital rectal examination (DRE) trial and they qualified for antibiotic therapy. Suspicion of a tumor was diagnosed in 69 (1.59 %) patients of the study group at the first visit after the DRE trial and they qualified for biopsy of the prostate after the PSA trial and TRUS at the second visit. Therefore, 4,216 patients took part in the clinical trial. In the course of 12 months 392 patients were excuded from the study for different reasons: cardiac infarct, apoplexy, resignation without reason and change of address. According to the IPSS scale (International Prostate Symptom Score) a small intensification of symptoms was diagnosed in 676 patients (16%), in 2,830 patients (67%) moderate and in 718 patients (17 %) considerable. Prostate cancer was confirmed histopathologically in 50 (1.15%) out of 69 patients who qualified for biopsy of the prostate. In 2,677 (70%) patients taking both alpha-blocker and finasteride, the progression of disease reduced, the micturation improved considerably and the mass of adenoma of the prostate diminished by 40%. However, in 956 (25%) patients taking only finasteride or finasteride + phytotherapy the mass of adenoma of the prostate diminished by 40%, too. When the medical trial was finished, 212 patients (5.02 %) of the study group who showed intensive symptoms of BPH and the finasteride and alfa-blocker treatment proved not to be effective enough qualified for surgical therapy. A total of 3,824 out of 4,216 (90.7%) patients finished the medical trial and 3,612 (85.6 %) were willing to continue the further therapy.