Objective: To examine the association between types of chronic conditions combinations and initial cancer treatment among elderly Medicare beneficiaries with localised prostate cancer. Methods: A population-based retrospective cohort study was conducted using the Surveillance, Epidemiology and End Results (SEER)-Medicare linked database. The study cohort consisted of elderly men (≥ 66 years) with localised prostate cancer diagnosed between 2002 and 2009 (N = 98,264). The initial cancer treatment received during the 6 months after cancer diagnosis consisted of (i) radical prostatectomy (RP); (ii) radiation therapy (RT); (iii) hormone therapy; and (iv) no treatment. Pre-existing chronic conditions were classified into the following eight groups: (i) only cardiometabolic conditions (CM); (ii) only mental health conditions (MH); (iii) only respiratory conditions (RESP); (iv) CM and MH; (v) CM and RESP; (vi) MH and RESP; (vii) all three conditions, CM, MH and RESP; and (viii) none of the three types of conditions. Results: Only 20% did not receive any cancer treatment; 47.4%, 22.1% and 10.5% received RT, RP, and hormone therapy, respectively. In multinomial logistic regression, elderly men with only RESP were more likely to receive RP as compared with those with all the three types of chronic conditions; those with only CM, only RESP, CM and MH or CM and RESP were more likely to receive RT. No significant associations were observed between the receipt of hormone therapy and types of chronic conditions. Conclusions: A significant proportion of elderly men with chronic conditions have received aggressive initial cancer treatment. Our study findings suggest a conservative approach for the initial prostate cancer treatment among elderly men with significant chronic conditions and localised prostate cancer.