PURPOSE: We compared prostate-specific antigen (PSA) reduction after performing transurethral resection of the prostate (TURP) according to a preoperative PSA value of 4 ng/ml and analyzed the meaning of elevation of the preoperative PSA value over 4 ng/ml. MATERIALS AND METHODS: We investigated the PSA level and prostate volume by transrectal ultrasonography (TRUS), urine flow rate, residual urine volume, and international prostate symptom score (IPSS) preoperatively and at 1 year after performing TURP in 61 clinically diagnosed BPH patients who had lower urinary tract symptoms (LUTS). We enrolled the 61 patients into 2 groups according to their preoperative PSA level relative to 4 ng/ml and compared the PSA reduction ratio (postoperative PSA level/preoperative PSA level), prostate volume reduction ratio, preoperative prostate volume, resected prostate volume, preoperative residual urine volume, preoperative maximal flow rate, and IPSS in each group. RESULTS: In the preoperative PSA group > or =4 ng/ml, the PSA reduction ratio was significantly lower than the PSA group <4 ng/ml and there were significant differences between the two groups in total IPSS, obstructive score, and preoperative maximal urine flow rate but no significant differences in preoperative prostate volume, prostate volume reduction ratio, or resected prostate volume. CONCLUSIONS: Marked PSA reduction after performing TURP was achieved in members of the preoperative PSA group > or =4 ng/ml, who are expected to have more severe bladder outlet obstruction (BOO).