OBJECTIVES: According to the National Cancer Institute (INCA 2008), breast cancer (BC) is the malignant neoplasia which more affects Brazilian women (estimated 49,400 cases, with a crude incidence rate of 50.71 cases per 100 thousand women). Moreover, Health Ministry data shows that the mortality rate of the disease is increasing, in contrast developed countries, such as US (New England Journal of Medicine, 2005). This mortality may be partially explained by the advanced stages of the disease at diagnosis (III and IV), which represent 50% of new identified cases in Brazil (INCA 2005). This may be a result of population low awareness of BC and the importance of early detection. Thus, the objective of this study is to assess women's knowledge of this neoplasia, their perception of its risks and methods of diagnosis. METHODS: Quantitative study performed through personal and individual interviews. A representative sample of the population (N=552) was used, composed by women between 30 and 60 year-old living in 4 capitals of Brazil (Rio de Janeiro, Sao Paulo, Porto Alegre and Salvador). A 20-question structured questionnaire was applied. RESULTS: Ninety percent of interviewed women understand cancer as a disease that brings health risks, highlighting breast (79%) as the most threatening cancer. The majority pointed out self breast examination (82%) as the best diagnostic method for BC early detection, followed by mammography (35%). The main information sources of this neoplasia, which were spontaneously mentioned were: television shows (80%), hospitals (28%), and newspapers (22%). CONCLUSIONS: 79% of all Brazilian women are aware of the threat BC means to their health, but only some of them see mammography (35%) as a method that most importantly can increase the chance of an early diagnosis. These results will support informative continuous campaigns about the importance of early detection aiming to give population a greater chance of cure.