Introduction: Lymphedema is a chronic disease characterized by the progressive accumulation of protein-rich fluid within the interstitial and fibro-adipose tissues, exceeding the capacity of the lymphatic system. The gold standard for its treatment is the conservative method of complex decongestive therapy, which includes manual lymph drainage, four-layer bandaging, exercises and skin care instructions. The aim is to examine retrospectively the outcomes of therapeutic procedures in reducing arm volume and increasing shoulder range of motion in patients with arm lymphedema and to investigate the relationship between characteristics such as age and the stage of lymphedema on therapy effectiveness. Subjects and Methods: The study includes 118 female patients with arm lymphedema, with an average age of 60±11 years, who were treated at the Clinical Hospital Center Rijeka from 01/January/2021 to 31/December/2023. All patients underwent complex decongestive therapy for 10 working days. Baseline characteristics were collected, and arm volume and shoulder range of motion were measured on the first and tenth day of therapy. Results: The therapy significantly reduced arm volume (p<0,001) and improved shoulder mobility (p<0,001). Greater therapy effectiveness was observed in older patients (p 0,002, rₛ-0,28) and those with a higher stage of lymphedema (p<0,001, rₛ-0,45). Lower therapy effectiveness was noted in patients who received hormone therapy (p=0,002). Shoulder movement restriction was not dependent on the type of surgery, lymphedema stage, or time from operation to therapy. Although therapy success was not dependent on the presence of muscle atrophy, it was higher in patients with a positive Stemmer sign (p<0,001). Erysipelas occurred in 7.63% of patients and was associated with a greater reduction in arm volume (p=0,001). Conclusion: Complex decongestive therapy reduces arm swelling and improves mobility in patients with arm lymphedema following breast cancer surgery. Factors influencing therapy success have been identified, but further research is needed to understand better the mechanisms of treatment.