Complications after 2-stage tissue expander/implant breast reconstruction have been studied as outcomes of a single procedure. We separately evaluated complications after the second stage and assessed factors associated with the outcomes of the second stage of breast reconstruction.Patients who underwent immediate 2-stage breast reconstruction between February 2010 and April 2017 were retrospectively reviewed. Patient demographics, surgical factors of the first stage of breast reconstruction, and complications and number of revision surgeries after the second stage were recorded. Factors associated with postoperative complications were analyzed, and a risk-scoring system was devised.We analyzed 619 patients who underwent 653 immediate 2-stage breast reconstructions. Multivariate analysis showed that complications were associated independently with smoking history, radiotherapy, and a final inflation volume of 450 mL or greater. Each factor contributed 1 point in the creation of a risk-scoring system. The overall complication rate was increased as the risk score increased (1.2%, 4.7%, and 16.0% for 0, 1, and 2 risk scores, respectively, P < 0.001). Revision operation rate was also significantly different across the 3 groups (0.2%, 1.6%, and 12.0% for 0, 1, and 2 risk scores, respectively, P < 0.001). The area under the receiver operating characteristic curve was 0.732 and 0.731 for the logistic regression model and risk-scoring system, respectively (P = 0.975).In the second stage of immediate 2-stage tissue expander/implant breast reconstruction, the rate of complication and revision surgery can be predicted by a novel risk-scoring system. Greater attention and preventive measures for complications are needed for high-risk patients.