Background: There has been a marked increase in the use of contralateral prophylactic mastectomy (CPM) for women with unilateral breast cancer. Previous studies on quality of life (QoL) measures for women who have undergone CPM are mixed. Most surveys were conducted only post-operatively. This analysis reports QoL changes within the same patient before and after surgery, using a validated tool. Methods: This study includes women who were prospectively enrolled in the University of Iowa Breast Molecular Epidemiologic Resource. We included all women who had mastectomy on the affected side. Patients completed a validated QoL survey (FACT-B) which covered: overall QoL and additional cancer-specific concerns. Responses followed a five-point scale. Surveys must have been completed any time before surgery and 6-18 months after surgery. A Fixed Effects linear regression model was used to discern within-person changes in QoL measures before and after surgery. Analysis was stratified by unilateral mastectomy (UM) or CPM. Results: The study cohort included 34 women, 17 received CPM and 17 received UM. Mean age was 61.5 for women who chose UM and 50.6 for women who chose CPM (p <0.001). There were no differences in baseline QoL measures between the two groups. After surgery, both groups felt less nervous, though the change in the CPM group was greater (p<0.001). There were no other differences for the UM group in pre-post QoL measures. Women undergoing CPM did have QoL decrements (Table). Conclusions: Women who chose CPM feel less nervous after surgery. However, these women lose some sense of femininity and are more likely to experience physical post-operative sequelae. This adds to knowledge that can be used to counsel women about physical and emotional costs associated with CPM that manifest 6-18 months after surgery.