Postmastectomy syndrome (PMES) is considered one of the most frequent complications after radical operations in patients with breast cancer (BC).The aim of the study was to identify risk factors and develop preventive measures for PMES after radical operations in BC patients.Materials and methods. The immediate results of surgical treatment of 147 women with BC who underwent radical surgery were analyzed: the frequency of postoperative edema and PMES depending on the initial clinical and pathological parameters and treatment features using descriptive statistics, χ2 criterion, and correlation analysis.Results. PMES during the observation period was diagnosed in 17 (11.6 %) patients, including: I st. – in 7 (4.8 %); II st. – in 9 (6.1 %) and III st. in one case (0.7 %). In most cases, its development was associated with postoperative edema, which was detected in the early postoperative period in 15 (88 %) of these patients. The dependence of the incidence of PMES on BMI and the age of patients with a tendency to increase it with the use of adjuvant radiation therapy and decrease with primary breast plastic surgery has been established. The use of a complex of preventive measures led to a decrease in the frequency of PMES (from 17 % to 2 %).Conclusions. In patients with BC, a frequent complication of radical surgery is postoperative edema of the upper limb and / or PMES, the risk of which increases with increasing age and BMI, as well as with the use of adjuvant radiation therapy. The use of a complex of preventive measures helps to significantly reduce the frequency of these complications