Breast cancer is one of the most common illnesses affecting women. Treatment is most commonly an operating procedure when only a part of the breast is removed together with tumor, and mastectomy or complete breast removal. In addition to surgical treatment, chemotherapy, radiotherapy, hormonal and biological therapy are also used as therapy. The essential treatment procedure is a physical therapy that needs to be started as soon as possible. The aim of the final undergraduate thesis is to describe the application and effect of complete decongestive therapy in the treatment of lymphedema after mastectomy. Physiotherapy begins with the patient's status based on the data collected and a therapy plan should be made individually for every person considering his/her condition, age, interest and possibilities. The most common system whose function is impaired after a mastectomy is a lymphatic system where there is a possibility of lymph edema. Lymph edema is treated with therapy called complete decongestive physiotherapy and consists of manual lymph drainage, compressive bandaging, exercise, skin care and education. Education is carried out to better enable a person to function in everyday activities after coming home and thus improving the quality of life.