OBJECTIVES: The first year after cancer diagnosis is a period of intensive treatment and high cost. Our objective is to estimate the first year costs for patients initially diagnosed with one of the 19 most common cancers in Ontario between 1997 and 2007. METHODS: We selected patients who were diagnosed at 19 years of age or older, with valid ICD-O and histology codes, who survived more than 30 days after diagnosis, and had no second cancer within 90 days of the initial cancer from the Ontario Cancer Registry (N= 412,787). We linked these patients to health care administrative databases, and radiation therapy data from Cancer Care Ontario. We defined the health care resources to be costed and developed suitable costing methodologies. We examined health care resource use and calculated mean costs for each type of cancer in the first year after diagnosis. RESULTS: Patients with myeloma and brain cancer incurred the highest mean first-year costs ($71,892 and $65,629, respectively); patients with melanoma, uterine and prostate cancers had the lowest mean costs ($21,050, $29,115 and $29,309 respectively). The most costly resources for all cancer types were hospitalizations (38% of total costs) and physician services (28% of total costs). Surprisingly, chemotherapy and radiation therapy contributed very little to the total (4% and 1%, respectively). Previous research on first-year costs for patients aged 65+ in the US also found that brain and other nervous system cancers had the highest cost of care while melanoma of the skin had the lowest cost; hospitalization was also the costliest resource. CONCLUSIONS: The first-year costs of cancer care in Ontario are substantial and vary by tumour site. Hospitalizations and physician services comprise a large portion of the costs for all cancer types. These estimates will improve the quality of future cancer-related economic evaluations and are of value to researchers and policy makers.