AIM: To retrospectively assess the acute and long-term toxicity using aromatase inhibitors (AI) therapy concurrently with hypofractionated radiotherapy (HFRT) in breast cancer patients. METHODS: From November 1999 to October 2007, 66 patients were treated with breast HFRT and concurrent AI. In 63 patients (95.5%), HFRT delivered a total dose of 32.5 Gy to the whole breast within 5 wk (five fractions, one fraction per week). Other fractionations were chosen in three patients for the patients’ personal convenience. A subsequent boost to the tumor bed was delivered in 35 patients (53.0%). Acute toxicities were scored according to the Common Toxicity Criteria for Adverse Events v3. Late toxicity was defined as any toxicity occurring more than 6 mo after completion of HFRT and was scored according to the Late Effects Normal Tissue Task Force-Subjective, Objective, Management and Analytic scale. RESULTS: At the end of the HFRT course, 19 patients (28.8%) had no irradiation-related toxicity. Acute grade 1-2 epithelitis was observed in 46 patients (69.7%). One grade 3 toxicity (1.5%) was observed. With a median follow-up of 34 mo (range: 12-94 mo), 31 patients (47%) had no toxicity, and 35 patients (53%) presented with grade 1-2 fibrosis. No grade 3 or greater delayed toxicity was observed. CONCLUSION: We found that AI was well tolerated when given concurrently with HFRT. All toxicities were mild to moderate, and no treatment disruption was necessary. Further prospective assessment is warranted. AIM: To retrospectively assess the acute and long-term toxicity using aromatase inhibitors (AI) therapy concurrently with hypofractionated radiotherapy (HFRT) in breast cancer patients. METHODS: From November 1999 to October 2007, 66 patients were treated with breast HFRT and concurrent AI In 63 patients (95.5%), HFRT delivered a total dose of 32.5 Gy to the whole breast within 5 weeks (five fractions, one fraction per week). Another fractionations were chosen in three patients for the patients’ personal convenience. boost to the tumor bed was delivered in 35 patients (53.0%). Acute toxicities were scored according to the Common Toxicity Criteria for Adverse Events v3. Late toxicity was defined as any toxicity occurring more than 6 mo after completion of HFRT and was scored according To the Late Effects Normal Tissue Task Force-Subjective, Objective, Management and Analytic scale. RESULTS: At the end of the HFRT course, 19 patients (28.8%) had no irradiation-related toxicity. One grade 3 toxicity (1.5%) was observed. With a median follow-up of 34 mo (range: 12-94 months), 31 patients (47% No grade 3 or greater delayed toxicity was observed. CONCLUSION: We found that AI was well tolerated when given concurrently with HFRT. All toxicities were mild to Moderate, and no treatment disruption was necessary. Further prospective assessment is warranted.