There is little, if any, difference in disease-free or overall survival for patients with stage I and II breast cancer treated by either breast conservation therapy or mastectomy. With either treatment, there may be cosmetic and functional problems related to arm edema, limited shoulder motion, and shoulder pain. The extent to which factors such as surgery, radiotherapy, systemic therapy, and patient characteristics affect development of arm edema, limited shoulder motion, and shoulder pain is not well documented. We undertook a prospective study of arm edema, limited shoulder motion, and shoulder pain in every patient (N = 331) seen during a 6-month period for follow-up after radiotherapy postlumpectomy or mastectomy for primary breast cancer. Local treatment included lumpectomy and breast irradiation with (n = 232) or without (n = 97) axillary dissection. Ten other women underwent mastectomy and postoperative radiotherapy. Doses to each region treated were 50 Gy in 25 fractions. The operative area was treated with an additional 1,000 Gy in approximately 60% of patients. Twelve patients received axillary irradiation without axillary dissection, and 11 patients received supraclavicular irradiation. Chemotherapy with or without tamoxifen was used in 71 patients and tamoxifen alone was used in 150 patients. One hundred ten patients did not receive any adjuvant therapy. Ipsilateral arm edema occurred in 20 women (6.0%), limited ipsilateral shoulder motion in 5 (1.5%), and ipsilateral shoulder pain in 5 (1.5%). Edema was mild (1+) in 15 patients and moderate (2+) in five patients. Multivariate analysis revealed that the risk of arm edema was significantly increased in black women (p = 0.005, 4/18 versus 16/313 whites) and with mastectomy (p = 0.048, 2/10 versus 18/321 with lumpectomy). There is a low incidence of arm edema, decreased range of motion of the ipsilateral shoulder, and shoulder-arm pain in patients undergoing postlumpectomy or postmastectomy radiotherapy. The risk of arm edema is increased in black women and in patients after mastectomy as opposed to lumpectomy.