purpose: to study frequency of the knowledge and practice of breast self-examination (bse), characterizing some factors that may interfere in its practice. method: during one month, 505 women, who were patients of the "centro de saúde escola-marco (belém-pará)", were interviewed, answering questions about the practice and knowledge on breast self-examination and associated factors. statistical analysis was perfoprmed using the c2 test. results: 96% of the women knew about bse. among these, 58.9% learned about it via the midia. however, the way that provided the most correct practice was medical orientation (37.5%). only 21.8% of the women performed the examination monthly. the main reason for the low adhesion was unfamiliarity with the technique (48.2%). women between 30 and 39 years presented the highest percentage of monthly practice (30.2%). the women (58.2%) who carried out the monthly examination had at least an incomplete high school degree. in 58.7% of the cases, the gynecologist did not stimulate the practice of the bse. conclusions: although bse is known by practically all the interviewees, more than one third of them do not practice it. the main reason of the low adhesion was the unfamiliarity with the technique. level of instruction and age of the women interfered in the practice of bse, but presence of breast cancer cases in the family did not.