Breast cncer incidense has been increasing in recent years and progress has been made in treatment modalities and techniques. Mobilization of the involved arm is recommended to prevent limitation of the range of motion (ROM) in shoulder in patients who had breast surgery and axillary dissection. Therefore, active-assistive and gentle passive Rom exercises should be initiated as early as possible after surgical procedures. Achievement of full ROM in shoulder is also a necessity to position patient during postoperative radiation therapy administration. Exercise program given in the postperative period is also helpful in the prevention of lymphedema which may develop postoperatively and following radiation therapy. Patient education on home care principles and possible compications is an essantial factor in rehabilitation. Sixty-two patients have been included in the rehabilitation program initiated before the commencement of radiation therapy in a co-operative study performed by Departments of Physical Therapy and Rehabilitation, Radiation Oncology and General Surgery. Mean age of the patients was 50 years ranging between 33 and 76 years. Shoulder pain, tenderness, ROM in shoulder joint, differences in arm and forearm circumferantial measurements were taken before radiation therapy, weekly during radiation therapy and a month after the completion of radiation therapy. Mean intervalbetween operation and inclusion in the program was 3.6+2.5 months. Sixty-six percent of the patients had modified radical mastectomy and 34 percent of the patients had breast conserving surgery. None had radical mastectormy. Before the initation of the rehabilitation program, 19 patients (31%) had normal Rom while shoulder limitation was detected in 43 patients (69%). A month after the completion of radiation therapy, normal ROM was detected in 39 patients (63%) and limitation of Rom in 23 (37%). Statistically significant improvements have been achieved after the rehabilitation program in terms of pain in shoulder region, tenderness level and ROM in the shoulder. In conclusion, medical rehabilitation plays a major role in the prevention of complications and should be initiated as early as possible.