The monthly practice of breast self-examination (BSE) can result in the early diagnosis of breast cancer. To explore factors that influence women's habits in the practice of BSE, we interviewed 616 women using an interactive computer program. We found that these women were more likely to practice BSE on a frequent basis if they were living with their sexual partner, had been shown how to perform BSE, and were confident in their examination technique. Women with a maternal history of breast disease were also more likely to practice monthly BSE. Unlike past reports that women with formal education beyond high school practice BSE more frequently than less-educated women, our study showed no association between monthly BSE practice and formal education. Contrary to our hypothesis that BSE practice was associated with the practice of other preventive health activities, our study did not demonstrate such a relationship. These findings suggest that demonstrating BSE at the periodic health examination may help increase the number of women practicing BSE on a frequent basis.