Background Comparing relative costs for androgen deprivation therapy (adt) protocols in prostate cancer (pca) requires an examination of all health care resources, not only those specific to pca. The objective of the present study was to use administrative data to estimate total health care costs in a population-based cohort of pca patients.Methods Patients in Ontario with pca who started 90 days or more of adt at age 66 years or older during 1995–2005 were selected from cancer registry and health care administrative databases. We classified patients (n = 21,818) by regimen (medical castration, orchiectomy, anti-androgen monotherapy, medical castration with anti-androgen, orchiectomy with anti-androgen) and indication (neoadjuvant, adjuvant, metastatic disease, biochemical recurrence, primary nonmetastatic). Using nonparametric regression methods, with inverse probability weighting to adjust for censoring, and bootstrapping, we computed mean 1-year, 5-year, and 10-year longitudinal total direct medical costs (2009 Canadian dollars).ResultsMean first-year costs were highest for metastatic disease, ranging from $24,400 for orchiectomy to $32,120 for anti-androgen monotherapy. Mean first-year costs for all other indications were less than $20,000. Mean 5-year and 10-year costs were lowest for neoadjuvant treatment: approximately $43,000 and $81,000 respectively, with differences of less than $4,000 between regimens. Annual costs were highest in the first year of adt. Orchiectomy was the least costly regimen for most time periods, but was limited to primary and metastatic indications. Outpatient drugs, including pharmacologic adt, accounted for 17%–65% of total first-year costs.Conclusions Compared with combined therapies, the adt monotherapies, particularly orchiectomy when clinically feasible, are more economical. Our methods exemplified the use of algorithms to elucidate clinical information from administrative data. Our approach can be adapted for other cancers to expand the range of studies using Canadian administrative data.