We have been performing TRUS-guided transperineal prostate brachytherapy with I-125 for prostate-confined adenocarcinoma since October 2003. We examined prostate volume using CT scanning on Day 1, Day 15, and Day 30 in the initial 15 patients, and investigated time-dependent changes of edema associated with I-125 prostate brachytherapy. Prostate volume had increased to 173% of the average on the first day after implantation. Improvements in the swelling of the prostate showed decreases in 30% in the first 2 weeks (Days 1-15) and 12% in the second 2 weeks (Days 15-30). V100 and D 90% showed statistically significant increases of 5.5% and 8.4% in the first 2 weeks after implantation and 2.3% and 5.2% in the second 2 weeks (Days 15-30). We considered one month a suitable time at which to calculate post-planning because V100 and D 90% changed little statistically.