This study investigated the effect of a BSE training program on women's knowledge, attitudes, and behavior regarding BSE. Postal questionnaires were sent to 629 women who had participated in 1998-2000 in the BSE training program run by Ribe County, Denmark, and to a local matched control group of the same size selected through personal registration numbers. Response rates were 77% and 56%, respectively. A significantly greater number of women who had attended BSE training reported that they knew how and when to do BSE, and what they should do if they discovered breast changes (97% compared to 66% in control group). Similar proportions in each group felt confident of finding any breast changes (57%) and believed that routine BSE can influence the chances of recovery from breast cancer (90%). There were also no significant differences between the intervention and control groups in the reporting of anxiety as a result of performing BSE (24% and 17%, respectively). The intervention group was significantly more likely to perform BSE regularly (66% compared to 52% in control group) and to use a more correct technique (44% compared to 20% in control group). It was concluded that a formal training program increases the likelihood of regular BSE performance with a correct technique.