Between August 1985 and March 2004, we performed transurethral resection of the prostate (TURP) in 18 patients with benign prostatic hyperplasia (BPH) whose prostatic volume was larger than 100 ml. We divided the patients into two groups. Group A consisted of a total of 14 cases: 10 cases whose mean prostate volume was 114 ml (100 to 137 ml) and 4 cases whose prostate volume was not measured before TURP but whose mean resected prostatic tissue weight was 113 g (105 to 118 g). Group B consisted of 4 cases whose mean prostate volume was 110 ml (101 to 133 ml). Patients in group B underwent interstitial laser coagulation of the prostate (ILCP) followed by oral chlormadinone acetate (CMA) therapy (50 mg/day); TURP was performed 6 months later, once the prostate volume had shrunk to an average of 76 ml (66 to 91 ml). Mean resected weights and operation times were: group A, 93.1 g, 66.3 min; group B, 60.5 g, 55.7 min. There were 12 blood transfusion cases (85.7%; intraoperative) in group A, and 1 (25.0%; POD 1) in group B. Accordingly, this preoperative treatment was considered a safer method of TURP for BPH 100 ml or more. There were no cases of TURP syndrome or death in either group.