Background Adjuvant whole breast radiotherapy has encountered a remarkable evolution during the past decades. Ultra-hypofractionation radiotherapy represent the next generation of hypofractionation trials which is associated with reduced health care expenditure and enhanced patient convenience. The aim of the study is to evaluate the efficacy and toxicity of adjuvant ultra-hypofractionated one week whole breast irradiation. Material and Methods Over 18 months, 100 patients with high-risk early-stage breast cancer who underwent breast conservative surgery, where divided into two groups, Arm A received 40 Gy in 15 fractions (over 3 weeks)and Arm B received 26 Gy in five fractions (over 1 week)to the whole breast. Treatment outcome was assessed by late toxicity, loco-regional control and distant metastasis. Results After a follow-up period of 3 years, late toxicity was documented in 6 patients (12%) in Arm A, in comparison to 9 patients (18%) in Arm B. After a median follow-up of 42.3 months, no significant difference was reported between both arms, regarding loco-regional control, incidence of distant metastasis and all-cause mortality, p=1.0, p=1.0 and p=0.55, respectively. Conclusion Ultra-hypofractionated adjuvant whole breast one week radiotherapy is a well-tolerated, effective and less time-consuming schedule