['The use of radiation therapy (RT) after breast-conserving surgery (BCS) is inconsistent in patients treated with hormonal therapy (HT). We sought to identify factors influencing the decision to use RT in this setting.', 'Patients in the North American Fareston vs. Tamoxifen Adjuvant (NAFTA) trial who had BCS were evaluated for factors influencing the use of RT using univariate and multivariate analyses.', 'Of the 1,811 patients enrolled in the NAFTA trial, 1,222 (67.4%) had BCS. Of these, 241 (19.7%) did not have RT. There were no significant differences in tumor grade, lymphovascular invasion, estrogen receptor status, or nodal status between those who received RT and those who did not. On univariate analyses, patients who did not receive RT were more likely to be older (median 72 versus 66 years, P < .001), have larger tumors (median 1.35 versus 1.10 cm, P = .009), and be progesterone negative (18.3% versus 13.1%, P = .048). Surgeons in the West were most likely to omit RT, whereas those in the Midwest were least likely to omit it (26.7% versus 7.2%, P < .001). Surgical oncologists were more likely to omit RT after BCS than general surgeons (21.8% versus 13.7%, P < .001). Academic affiliation (P < .001), number of breast procedures performed per year (P = .017), and the percentage of breast practice (P = .019) also correlated with whether or not RT was used. On multivariate analysis, patient age (P < .001), geographic region (P = .006), and surgeon specialty (P = .027) remained significant.'] Is the use of radiation therapy after breast-conserving surgery in hormonally treated breast cancer patients dependent on patient age , geographic region , and surgeon specialty?