BACKGROUND: Patients with breast cancer with pathologic N3 (pN3) lymph node status have been proven to have a poor prognosis. This study aimed to establish a nomogram to predict overall survival (OS) in patients with pN3 breast cancer. MATERIALS AND METHODS: The eligible patients from the Surveillance, Epidemiology, and End Results (SEER) database were randomly divided into training and validation cohorts. χ tests and survival curves were performed to define the consistency between these 2 cohorts. Univariate and multivariate logistic regressions were carried out to identify the independent clinicopathologic factors of patients with pN3 breast cancer. A nomogram was developed and validated internally and externally by a calibration curve and compared with the seventh edition American Joint Committee on Cancer TNM staging classification in discrimination ability. RESULTS: Race, age at diagnosis, marital status, grade, T stage, N stage, breast cancer subtype, surgery, radiotherapy, and chemotherapy were independent predictive factors of OS in pN3 breast cancer. We developed a nomogram to predict 1-, 3-, and 5-year OS and further validated it in both cohorts, demonstrating better prediction capacity in OS than that of the seventh edition American Joint Committee on Cancer TNM staging classification (area under the curve in the receiver operating characteristic curve, 0.745 and 0.611 in the training cohort and 0.768 and 0.624 in the validation cohort, respectively). CONCLUSION: We have developed and validated the first nomogram for predicting the survival of pN3 breast cancer. This nomogram accurately and reliably predicted the OS of patients with pN3 breast cancer. However, more prognostic factors need to be further explored to improve the nomogram.