Lymphedema of the upper extremity is one of the most distressing and unpleasant for the patient of all the complications of treating breast cancer. The incidence of lymphedema was studied in 277 breast cancer patients according to age, lesional location, interval since diagnosis, pathological TNM stage and a variety of treatment. Lymphedema was present in 61 of 277 breast cancer patients (22.0%). Sixteen (26.3%) of these case were in the group of 41∼45 years of age. The incidence of lymphedema in the breast cancer patients was greater in the group of left side (24.7%), upper inner location (31.6%), stage IV (41.4%) and mastectomy plus radiation therapy (66.7%). Twenty-six patients (42.6%) developed a upper extremity lymphedema during the immediate period (first 1 month).