OBJECTIVES: Patients with CRPC may be treated by urologists or oncologists. This study examined differences in total health care costs and prostate cancer-specific costs in patients treated by oncologists or urologists. METHODS: A retrospective study design used medical and pharmacy claims (2001-2007) to identify patients with CRPC from a large US managed care health plan. Patients were stratified based on the specialist providing treatment following castration; an oncologist (with/without a urologist, ONC), and a urologist without an oncologist (URO). A 6-month baseline period was used to assess patient characteristics and initial clinical status; a variable follow-up period (until disenrollment or December 31, 2008) was used to assess total health care costs. Lin’s regression was used to assess costs adjusting for the variable follow-up and patient and treatment characteristics. RESULTS: A total of 995 URO and 1590 ONC patients with CRPC were identified. Mean age was higher in URO patients than in ONC patients (75.5 vs. 71.1 years, p<0.001). The URO cohort had a lower average Charlson comorbidity score (3.7 vs. 4.9, p<0.001), fewer comorbid illnesses (10.1 vs. 11.1, p<0.001), and were less likely to have other cancers (17.7% vs. 27.4%, p<0.001) or to have had hormones, chemotherapy, radiation treatment during the baseline period. After multivariate adjustment, mean total health care costs during the first year were $31,792 (URO), $54,306 (ONC with chemotherapy, p<0.05), and $30,894 (ONC without chemotherapy); during 6-years of follow-up, cumulative costs rose to $86,706 (URO), $168,794 (ONC with chemotherapy), and $114,180 (ONC without chemotherapy), p<0.05 for all. A similar pattern was observed for prostate cancer-specific cumulative costs. CONCLUSIONS: CRPC patients treated by oncologists, particularly patients with chemotherapy, had higher total and prostate cancer-related health care costs than patients treated by urologists.