Background: This study aimed to determine the impact of complex decongestive therapy applications on upper extremity function in breast cancer patients who developed adhesive capsulitis after lymphedema. Methods: Thirty patients who developed adhesive capsulitis due to lymphedema were divided into two groups as study (n = 15) and control (n = 15) groups. Both groups received 20 minutes of exercise five days a week for three weeks using a Biodex isokinetic dynamometer, as well as a hot pack and TENS (Transcutaneous Electrical Nerve Stimulation) treatment to the shoulder joint. The study group received 45 minutes of intensive decongestive therapy along with the adhesive capsulitis treatment. The visual analogue scale was used to assess pain, circumference, and volumetric measurements were used to assess edema, and the Arm, Shoulder, and Hand Problems Questionnaire (DASH: Disabilities of the Arm, Shoulder, and Hand) was used to assess upper extremity functionality. The shoulder range of motion was evaluated. Results: Both groups had improvements in pain (P < 0.001), shoulder joint range of motion (P < 0.001), and upper extremity functionality (P < 0.001) after the treatment. There was a significant decrease in circumference and volumetric measurements in the study group (P < 0.001). However, no differences were seen in measurements in the control group. Conclusions: The results showed that complex decongestive therapy was beneficial in reducing lymphedema in breast cancer patients who acquired adhesive capsulitis due to lymphedema. Consequently, the authors believe that supplementing conventional physiotherapy with complex decongestive therapy will benefit patients.