This paper reports the results of an open non-comparative clinical study of medicinal products with the purpose of estimating the therapeutic efficacy and safety of VENOTEKS hosiery used for the treatment of postmastectomy lymphedema in the upper extremities. A total of 30 women at the age from 27 to 73 (mean 59.2±11.02; median 60) years underwent radical breast surgery. All the patients presented with stage II lymphedema. Grade I postmastectomy oedema of the upper extremities (PMO) (the difference between the limb circumferences up to 2 cm) was documented in 12 patients, grade II PMO (the difference between the limb circumferences up to 2-5 cm) in 14 ones, and grade III PMO (the difference between the limb circumferences in excess of 5 cm) in 4 women. All the patients wore compression sleeves (26-32 mm Hg) during 30 days. The difference between the circumferences of the affected and intact upper extremities was estimated from the results of the measurement of the subcutaneous fat thickness at the levels of the mid-third of the forearm and the mid-third of the upper arm by means of ultrasound scanning. In addition, the number of the patients presenting with the subjective symptoms (pain, discomfort sensation, fatigue, impaired sensitivity, and reduced range of movements) was determined before and after the treatment. No phlebolymphotonic drugs were prescribed. Compression therapy was shown to cause the statistically significant reduction in the difference between the circumferences of the affected and unaffected extremities at all measurement levels. The decrease in the subcutaneous fat thickness was confirmed by calculations of the 95% confidence interval for the difference between the mean values. The number of the patients with subjective symptoms significantly decreased by the end of the 30 day period of the study. The results of the study indicate that wearing compression sleeves effectively reduces the severity of oedema and eliminates subjective clinical symptoms in the patients with postmastectomy lymphedema. It is concluded that compression therapy must be included in the combined treatment of this pathological condition.