Objective: Despite little survival benefit and potential for harm, contralateral prophylactic mastectomy (CPM) rates are increasing amongst early-stage breast cancer patients at low contralateral breast cancer risk. We developed a CPM decision aid (DA) and conducted a pilot implementation. Methods: Surgeons and oncologists recruited eligible patients considering CPM. Consenting patients received the DA, completed a questionnaire and participated in a semi-structured interview. Clinicians were interviewed at study close. Results: Eleven clinicians and 31 patients participated. Three themes emerged: perceived utility and impact of the DA, disagreement regarding timing of delivery and target population, and implementation strategies. Both women and clinicians found the DA valuable, indicating it confirmed rather than changed preferences. Women (all of whom raised CPM themselves), preferred offering the DA early in treatment discussions whilst clinicians favoured targeting women who enquired about CPM. Conclusion: A DA about CPM is feasible and acceptable, but questions remain about the role of DAs in these types of decisions where one option has limited medical benefit. Practice implications: Some women have a high need to make an informed choice about CPM. Tools to support this could include a DA with a clear recommendation against CPM and an explanation why.