Neoadjuvant chemotherapy (NAC) is an increasingly common approach in the treatment of breast cancer. The use of post-mastectomy RT (PMRT) remains standard in women who have persistent nodal disease (ypN+) after NAC followed by mastectomy (M). We evaluated the National Cancer Database (NCDB) to examine characteristics associated with appropriate use of PMRT in this population over a 10 year period. We identified women in the NCDB with invasive ductal carcinoma who underwent NAC, M, and were ypN+ between 2004-2014. We analyzed patient characteristics, demographics, and disease characteristics including clinical T and N stage at diagnosis, receptor status, margin status, tumor grade, and y-pathologic stage after NAC. Multiple logistic regression models were used to assess for associations with receipt of PMRT, and Kaplan Meier (KM) analysis to estimate effect on overall survival. A total of 12,098 patients met eligibility criteria. Median age was 55 years, 18.4% cN0 vs. 81.6% cN+, 17.7% were black race, 7.1% hispanic, 63.7% ER+, 12.9% triple negative (TN), and 8.0% margin+; all were ypN+. Overall, 71.9% of patients received PMRT, and the use of PMRT increased over time form 65.5 % in 2004-2006 to 73.3% in 2013-2014. On univariate analysis, the only socioeconomic/ demographic factor associated with receipt of PMRT was age: women ≤50 vs >50 were more likely to receive PMRT (73.7% vs 70.8%, P<0.0001). However multiple clinical factors were associated with use of PMRT. Patients with the following disease characteristics were more likely to receive PMRT: estrogen receptor ER+ vs. ER- (74.6% vs. 68.1%, P<0.0001), non-triple negative vs. triple negative (76.3% vs. 70.2%, P<0.0001), cN+ vs. cN0 (76.3% vs. 62.1%, P<0.0001), ypN2-3 vs. ypN1 (78.2% vs. 66.9%, P<0.0001), grade 2-4 vs. grade 1 (72.1% vs. 66.2%, P=0.002), and margin- vs. margin+ (72.2% vs. 68.7%, P=0.024). Pathologic T stage was not significant. On multivariate analysis, the following factors remained significantly associated with less use of PMRT: cN0 presentation vs cN+ (OR 0.48; CI: 0.42-0.56), ypN1 vs ypN2-3 (OR 0.54; CI: 0.48-0.62), and ER- vs ER+ (OR: 0.56; CI: 0.48-0.72). On KM analysis, median survival time was 91.3 months for those who did not receive PMRT vs. 103.6 months for those who did (P<0.0001). Our analysis demonstrates that many women with persistent ypN+ disease after NAC and M do not receive PMRT, despite an established benefit. While most demographic and socioeconomic factors were not associated with receipt of PMRT, a number of clinical factors were, including both clincal presenting and final yp nodal stage. Our findings point to a need for improved access to PMRT in this population, potentially including clinician education in this rapidly evolving area.