Aim: In the Present study the expected outcome of the mastectomy compared with perceived treatment outcomes based on self-efficacy in women with breast cancer. Method: In the current study, 300 female patients with breast cancer were studied before and after mastectomy using the general self-efficacy scale and expectancy outcome incongruence. Results: The finding yielded that there was significant difference between patients with the high and low self-efficacy based on the expectation of the result of surgery and perceived outcome of surgery. Similarly there is significant difference between the level of disease progression based on the expectation of the surgery outcome and perceived outcome of surgery. In addition, there was significant difference between breast tumor size based on the expected outcome of surgical treatment and perceived outcome of surgery. There was significant difference between elderly and non-elderly women self-efficacy. Conclusions: Results show the higher level of self-efficacy can be useful in establishing primary social adjustment but lead to underestimate the negative effects of surgery.