Objective: To analyze the correlations among comorbidity and overall survival (OS), biochemical progression-free survival (b-PFS) and toxicity in elderly patients with localized prostate cancer treated with 125 I brachytherapy. Methods: Elderly men, aged ≥65 years, with low-intermediate risk prostate cancer, were treated with permanent 125 I brachytherapy as monotherapy. Comorbidity data were obtained from medical reports using age-adjusted Charlson comorbidity index (a-CCI). The patients were categorized into two age groups (<75 and ≥75 years old), and two comorbidity score groups (a-CCI ≤3 and >3). Toxicity was scored with Radiation Therapy Oncology Group (RTOG) scale. Results: From June 2003 to October 2009, a total of 92 elderly patients underwent prostate brachytherapy, including 57 men (62%) with low-risk prostate cancer, and 35 men (38%) with intermediate-risk prostate cancer. The median age of patients was 75 years (range, 65-87 years). Forty-seven patients (51%) had a-CCI ≤3 and 45 patients (49%) a-CCI >3. With a median follow-up period of 56 months (range, 24-103 months), the 5-year actuarial OS and b-PFS were 91.3% and 92.4% respectively, without statistical significance between two Charlson score groups. Toxicity was mild. None of the patients experienced gastrointestinal (GI) toxicity, and only 4 patiens (4%) experienced late genitourinary (GU) grade-3 (G3) toxicity. No correlation between acute GU and GI toxicity and comorbidity was showed (P=0.50 and P=0.70, respectively). Conclusions: Our data suggest that elderly men with low-intermediate risk prostate cancer and comorbidity can be considered for a radical treatment as 125 I low-dose rate brachytherapy. Objective: To analyze the correlations among comorbidity and overall survival (OS), biochemical progression-free survival (b-PFS) and toxicity in elderly patients with localized prostate cancer treated with 125 I brachytherapy. Methods: Elderly men, aged ≥65 years, with low-intermediate risk prostate cancer, were treated with permanent 125 I brachytherapy as monotherapy. Comorbidity data were obtained from medical reports using age-adjusted Charlson comorbidity index (a-CCI). The patients were categorized into two age groups (<75 and ≧ 75 years old), and two comorbidity score groups (a-CCI ≤ 3 and> 3). Toxicity was scored with Radiation Therapy Oncology Group (RTOG) scale. Results: From June 2003 to October 2009, a total of 92 elderly patients The median age of patients was 75 years (range, 65-87 years). Forty men (62%) with low-risk prostate cancer, and 35 men -seven patients (51%) had a-CC I ≤ 3 and 45 patients (49%) a-CCI> 3. With a median follow-up period of 56 months (range, 24-103 months), the 5-year actuarial OS and b-PFS were 91.3% and 92.4 None of the patients experienced gastrointestinal (GI) toxicity, and only 4 patiens (4%) experienced late genitourinary (GU) grade-3 (G3) toxicity. No correlation between acute GU and GI toxicity and comorbidity was showed (P = 0.50 and P = 0.70, respectively). Conclusions: Our data suggest that elderly men with low-intermediate risk of prostate cancer and comorbidity can be considered for radical treatment as 125 I low-dose rate brachytherapy.