Whether age is an independent prognostic factor in breast cancer is a matter of debate. This is a retrospective cohort study of 767 breast cancer patients, stages I-III, treated at the Hospital das Clínicas, Minas Gerais Federal University, Belo Horizonte, Minas Gerais State, Brazil, from 2001 to 2008, aiming to study the relationship between age and survival. We included variables related to patients, tumors, and types of treatment. Different sets of Cox models were used for survival analysis. Hazard ratios (HR) and 95%CI were calculated. The relationship between age and breast cancer survival did not change substantially in any of them. In the model that accounted for all variables, women aged 70 and older (HR = 1.51, 95%CI: 1.04-2.18), and 35 or younger (HR = 1.78, 95%CI: 1.05-3.01) had shorter cancer specific survival than patients aged between 36 and 69. In addition, older age, having at least one comorbidity, and being white were associated with a higher risk of dying from other causes. In conclusion, shorter breast cancer survival is expected among the youngest and oldest patients.