Objective: The objective of the present analysis was to determine the publicly funded health care costs associated with the care of breast cancer (BCa) patients by disease stage. Methods: Incident cases of female invasive BCa (2005–2009) were extracted from the Ontario Cancer Registry and linked to administrative datasets from the publicly funded system. The type and use of health care services were stratified by disease stage over the first 2 years after diagnosis. Mean costs and costs by type of clinical resource used in the care of BCa patients were compared with costs for a matched control group. The attributable cost for the 2-year time horizon was determined in 2008 Canadian dollars. Results: This cohort study involved 39,655 patients with BCa and 190,520 control subjects. The average age in those groups was 61.1 and 60.9 years respectively. Most BCa patients were classified as either stage I (34.4%) or stage II (31.8%). Of the BCa cohort, 8% died within the first 2 years after diagnosis. The overall mean cost per BCa case from a public payer perspective in the first 2 years after diagnosis was $41,686. Over the 2-year time horizon, the mean cost increased by stage: I, $29,938; II, $46,893; III, $65,369; and IV, $66,627. The attributable cost of BCa was $31,732. Cost drivers were cancer clinic visits, physician billings, and hospitalizations. Conclusions: Costs of care increased by stage of BCa. Cost drivers were cancer clinic visits, physician billings, and hospitalizations. These data will assist planning and decision-making for the use of limited health care resources.