Women's knowledge of breast cancer and their beliefs about susceptibility to breast cancer and benefits of breast self-examination were explored in relation to frequency of practice of breast self- examination. Previous findings indicated that knowledge and beliefs may affect the practice of preventive health behaviors. A self-report questionnaire was administered to 263 women contacted through sorotiy alumnae groups and Y.M.C.A. groups. Subjects were grouped according to levels of physical exercise (high, moderate, or none) and compared on knowledge and beliefs about breast cancer and breast self- examination (BSE) and practice of BSE. Data were analyzed using descriptive statistics and chi-square analysis. Results showed women overestimated the prevalence of breast cancer but were correctly aware that most lumps are not malignant. They generally were uninformed of the risk factors of breast cancer, except for a positive family history of breast cancer. The majority perceived themsleves as strongly susceptible to breast cancer and almost all perceived BSE as beneficial in reducing the threat of death from breast cancer.Only 37 percent of the women practiced breast self-examinatin regularly. No significant relationship existed between knowledge or beliefs and frequency of performance of BSE. Nor were there any significant differences in frequency of practice between the exercisers and nonexercisers. It may be concluded from this study that knowledge of breast cancer, beliefs about brest cancer and breast self-examination or engaging in regular physical exercise as a preventive health behavior do not affect the practice of breast self-examination.