From September 2003 to December 2005, 188 patients who visited our hospital and allied institutions for the purpose of prostate brachytherapy were administrated hormonal therapy for volume reductions before brachytherapy. The pretreatment and posttreatment of prostate volume using a transrectal ultrasound volumetric study and the types and duration of hormonal therapy were analyzed. We administered 91 patients with Luteinizing hormone-releasing hormone (LH-RH) agonist, 49 patients with anti-androgen (bicaltamide/flutamide), and 48 patients with maximum androgen blockade (MAB). The duration of the hormonal therapy was 1-3 months for 49 patients, 4-6 months for 59 patients, 7-9 months for 40 patients, 10-12 months for 32 patients, and over 13 months for 8 patients. Before the initiation of hormonal therapy, the mean prostate volume was 35.12 ml (11.04-78.71 ml), and the average of prostate volume before and after hormonal therapy was 36.79 ml and 24.79 ml, respectively (a 32.4% reduction). The prostate volume reduction rate was 32.0% for the LH-RH agonist only, 18.1% for the anti-androgen only and 41.2% for the MAB. No statistically significant difference was observed for the duration of hormonal therapy between 3 groups. A three-month course of the neoadjuvant LH-RH agonist indicated a sufficient volume reduction effectiveness for a large prostate volume.