OBJECTIVES: The aim of this study is to determine direct medical costs of treating patients with prostate cancer from the perspective of a Brazilian HMO. METHODS: An administrative database containing inpatient and outpatient claims of Unimed São Jose do Rio Preto, a HMO in São Paulo state with 131,064 beneficiaries, was reviewed from Jan/2004 to Dec/2013. Eligibility criteria were patients with a medical claim associated with prostate cancer (ICD-10 code C61) from Jun/2012 to Dec/2012, with more than 30-days of follow-up data. Diagnosis date for these patients were ascertained and they were followed until death or loss of follow-up, whichever comes first. Outcome was direct medical costs (DMC), calculated as the sum of the medical claims for each patient included in the analysis. DMC-per-year associated with prostate cancer was calculated and stratified by treatment choice (wait-and-see, local therapy, androgen deprivation, chemotherapy).  RESULTS: CONCLUSIONS: Patients with prostate cancer represent a significant economic burden to private payers, escalating as disease progresses. Patients starting chemotherapy may cost per year approximately 6 times the cost of patients in early stages of the disease.