Background Primary angiosarcoma of the breast (PAOB) is rare and institutional series have provided conflicting data on the effect of grade on prognosis. Patients and Methods Using a case listing session of Surveillance, Epidemiology, and End Results (SEER) 18 (1973-2010) we examined outcomes for patients with PAOB. Analyses were conducted with SEER∗Stat 8.1.2, Microsoft Excel 2007, and GraphPad Prism 6. Comparisons were made using the Fisher exact test and log rank test (Mantel-Cox); P values were 2-sided. Results Two hundred twenty-six women with PAOB were identified; median age was 49 (range, 15-107) years and 82% (185) were white. Seventy-two percent (162) had localized disease, 15% (34) regional disease, 7% (16) distant disease, and 6% (14) had unknown staging. Fourteen percent (32) had Grade 1, 24% (55) Grade 2, 30% (68) Grade 3 disease, and grade was unknown in 32% (72) of patients. Median overall survival (OS) for patients with localized, regional, and distant disease was 172, 24, and 16 months, respectively (P <.001). Median OS for patients with localized Grade 1 and 2 disease was not reached versus 36 months for Grade 3 disease (P <.001); 3-year OS was 89% (78) versus 47% (32). There was a strong trend for patients with Grade 3 disease to undergo mastectomy (44%, n = 30 vs. 23%, n = 20; P =.070) and 24% (55) of all patients received radiation. Radiation did not improve survival for localized Grade 1 and 2 disease (P =.676), or Grade 3 disease (P =.589); surgery and grade subgroups were too small for meaningful comparisons regarding radiation. Conclusion Histologic grade is a significant predictor of survival for patients with localized PAOB. Regardless of grade, adjuvant radiation did not confer a survival benefit for patients with localized disease.