Purpose: An increasing proportion of breast cancer patients undergo contralateral prophylactic mastectomy (CPM) to reduce their risk of contralateral breast cancer (CBC). Our goal was to evaluate CBC risk perception changes over time among breast cancer patients. Methods: We conducted a prospective, longitudinal study of women with newly diagnosed unilateral breast cancer. Patients completed a survey before and approximately 2 years after treatment. Survey questions used open-ended responses or 5-point Likert scale scoring (e.g., 5 = very likely, 1 = not at all likely). Results: A total of 74 women completed the presurgical treatment survey, and 43 completed the postsurgical treatment survey. Baseline characteristics were not significantly different between responders and nonresponders of the follow-up survey. The mean estimated 10-year risk of CBC was 35.7 % on the presurgical treatment survey and 13.8 % on the postsurgical treatment survey (p < 0.001). The perceived risks of developing cancer in the same breast and elsewhere in the body significantly decreased between surveys. Both CPM and non-CPM (breast-conserving surgery or unilateral mastectomy) patients’ perceived risk of CBC significantly decreased from pre- to postsurgical treatment surveys. Compared with non-CPM patients, CPM patients had a significantly lower perceived 10-year risk of CBC (5.8 vs. 17.3 %, p = 0.046) on postsurgical treatment surveys. Conclusions: The perceived risk of CBC significantly attenuated over time for both CPM and non-CPM patients. These data emphasize the importance of early physician counseling and improvement in patient education to provide women with accurate risk information before they make surgical treatment decisions.