The aim of this study was to give information about the evidence based radiation oncology in the treatment of operable breast cancer for specialists involved in the national public health. It was performed a review of the English language clinical studies published in the nineties, in which specific radiotherapy questions of operable breast cancer were debated. Clinical studies were classified according to the level of obtained evidence: randomized study (level I.), cohort study (level II.), retrospective study (level III.) and meta-analysis (mathematical synthesis of results). 1. Findings of one large randomized study indicate that lumpectomy plus irradiation is more beneficial than lumpectomy alone for women with ductal carcinoma in situ. Findings are supported by retrospective studies. 2. There are four complete published randomized studies comparing the outcome of conservative surgery alone to that of conservative surgery plus radiation for patients with stage I-II. breast cancer. The local recurrence rate is unacceptably high when random patients are treated without radiotherapy. Meta-analysis of these studies conferred statistically significant survival advantages on women receiving irradiation. In one randomized clinical trial the delivery of a 10 Gy boost to the tumor bed after 50 Gy to the whole breast significantly reduces the risk of early local recurrence. Additional follow-up evaluation and more evidence will be required to define the indications for boost irradiation. In one randomized trial with unselected patients there was a significant superiority in local control for whole breast irradiation compared to partial breast irradiation, but interim results of prospective studies with carefully selected women appear promising. 3. Findings of three randomized controlled clinical trials indicate that postmastectomy radiotherapy reduces mortality from breast cancer by preventing locoregional recurrences in node positive patients. One study examined the effect of radiation on overall survival by meta-analysis of earlier published randomized studies and demonstrated the reduction of breast cancer deaths in irradiated patients. 4. The value of irradiation of parasternal lymph nodes is uncertain by retrospective studies and is currently being studied in a large European randomized trial. After an adequate axillary lymphadenectomy the incidence of axillary recurrence is low and there is no indication for irradiation. Results of two retrospective studies indicate that irradiation of supraclavicular lymph nodes is beneficial in patients with four or more positive axillary lymph nodes. In summary, thank to the intensive clinical research in radiotherapy, the irradiation of patients with operable breast cancer is based on level I. scientific evidences in the majority of the cases. Results of randomized controlled clinical trials and meta-analyses indicate that radiotherapy is more than locoregional control: breast cancer deaths are reduced among irradiated patients.