Objective To investigate the long-term effects of complex decongestive therapy (CDT) on edema reduction in breast cancer-related lymphedema patients after axillary dissection, according to the initial volume of edema. Methods A retrospective review of 57 patients with unilateral arm after an axillary dissection for breast cancer was performed. The patients, treated with two weeks of CDT and self-administered home therapy, were followed for 24 months. Arm volume was serially measured by using an optoelectronic volumeter prior to and immediately after CDT; and there were follow-up visits at 3, 6, 12, and 24 months. Patients were divided into two groups according to the percent excess volume (PEV) prior to CDT: group 1, PEV<20% and group 2, PEV≥20%. Results In group 1, mean PEV before CDT was 11.4±5.0% and 14.1±10.6% at 24 months after CDT with no significant difference. At the end of CDT, PEV was 28.8±15.7% in group 2, which was significantly lower than the baseline (41.9±19.6%). The reduction of PEV was maintained for 24 months in group 2. Conclusion The long-term effects of CDT were well-maintained for 24 months, but there was a difference in progression of PEV between the two groups. The patients with more initial PEV showed significant volumereducing effects of CDT. In patients with less initial PEV, the severity of lymphedema did not progress to higher grades.