['To test the hypothesis that cross-linked hyaluronan gel (Hylaform) does not affect the quality of life (QOL) of prostate cancer patients undergoing radiotherapy.', 'Thirty-five patients with early stage prostate cancer underwent high-dose-rate brachytherapy to 2200 cGy and intensity modulated radiation therapy to 5040 cGy on a prospective study. Thirty patients received a single transperineal injection of 9-mL Hylaform between the prostate and rectum under transrectal ultrasound guidance immediately before the start of radiotherapy. Hylaform increased the separation between the prostate and rectum by 6-19 mm (median, 13 mm) at the start of radiotherapy. Five patients did not receive Hylaform and served as controls. We assessed gastrointestinal-related QOL using Expanded Prostate Cancer Index Composite Bowel Bother scores immediately before the start of and during the last week of radiotherapy.', 'At the beginning of intensity modulated radiation therapy, daily mean rectal doses were 74±8 cGy (mean±standard deviation) and 105±25 cGy (mean±standard deviation) with vs. without Hylaform, respectively (p=0.01). Expanded Prostate Cancer Index Composite Bowel Bother scores decreased by 0±3 (mean±standard deviation) and 11±14 (mean±standard deviation) in patients who did and did not receive Hylaform, respectively (p=0.03).'] Does cross-linked hyaluronan gel improve the quality of life of prostate cancer patients undergoing radiotherapy?