Ontario cancer patients' monthly out-of-pocket costs (OOPC) were assessed to determine whether these costs were problematic. A self-administered questionnaire was administered to breast (n = 74), colorectal (n = 70), lung (n = 68) and prostate (n = 70) cancer patients between October 2001 and April 2003. It measured categorical OOPC, which were analysed using linear regression modelling, to determine whether any of a variety of independent variables influenced OOPC. Monthly OOPC (mean, range) were: parking/fares ($47, $0-450), devices ($46, $0-2350), prescription drugs ($45, $0-1400), accommodation ($43, $0-1500), complementary and alternative medicine ($29, $0-5000), vitamins ($25, $0-400), homemaking ($14, $0-1000), family care ($12, $0-1200), homecare ($2, $0-330) and other ($8, $0-250), with the total averaging $213 ($0-5230). Imputed travel mileage costs added $372 ($0-6180). Most patients were well served by the current healthcare programmes. In multivariate analysis, variables influencing several OOPC categories were: tumour site, hospitalization, age, and number of clinic trips. Travel costs proved the most problematic, with patients under 65 years and without insurance more likely to have high OOPC. Education and income were not reliable predictors for high OOPC. Many of these costs were for items not traditionally covered by public healthcare financing systems, raising important issues around defining 'medically necessary' care and the role of government.