OBJECTIVES: To determine the cost and outcome related to breast cancer patients treated in a Brazilian OCC in Rio de Janeiro, Brazil. METHODS: This is a retrospective study of women with breast cancer treated at a private practice OCC in Rio de Janeiro, Brazil. All the patients were covered by Amil, a Brazilian HMO. Direct costs (DC) of 199 patients diagnosed since 2002 and followed to the end of 2009 were analyzed and correlated to clinical stage. We used Kaplan-Meier method to analyse patients' outcome. RESULTS: Forty-eight percent of women were diagnosed in stage I, 34% patients in stage II, and only 2.5% were diagnosed in stage IV, similar numbers to those seen in developed countries. The average DC of their medical care per patient was 21,658.94 USD for stage I compared to 48,295.29 USD for stage II, and were 63,662.06 USD for stage III and 63,697.33 USD for stage IV. We also observed that DC per patient-year increased according to clinical stage. In the first year, average cost was 15,183.85 USD for stage I, while it was 44,160.74 USD for stage IV. Those DC decreased along the years in all stages. For example, in the seventh year of follow-up, the average DC was only US$ 467.27 for stage I (2005 purchasing power parity index 1 USD = 1.4 BRL). The 5-year overall survival and progression free survival were 100% and 100% for stage I, 92.2% and 91.9% for stage II, 87.5% and 82.1% for stage III, and 60% and 60% for stage IV, respectively. CONCLUSIONS: Breast cancer accounts for a significant part of the health insurance budget. Later stage at diagnosis is associated with higher DC per patient-year of treatment, and lower probability of 5-year survival.