Treatment for breast cancer may result in the formation of palpable cords in the axillary region. Our aim was to evaluate cording incidence, risk factors, and association with upper extremity functional impairment and measured arm volume change. We included 308 patients with unilateral breast cancer prospectively screened for upper extremity lymphedema, symptoms and function. Patients were assessed pre- and post-operatively and at 3-8-month intervals with perometer arm measurements and the LEFT-BC questionnaire. Cording was determined by patient self-report. The cumulative incidence of cording and its association with clinicopathologic factors, upper extremity functional impairment, and measured arm volume change were analyzed. 31.5 % (97/308) of patients reported cording, with a cumulative incidence of 36.2 % at 24 months post-operative. Clinicopathologic factors significantly associated with cording by multivariate analysis included axillary lymph node dissection (p < 0.0001) and younger age at diagnosis (p = 0.0005). Cording was associated with increased functional impairment (p = 0.0018) and an arm volume increase of ≥5 % (p = 0.028). Cording following breast cancer treatment is common, and may occur beyond the post-operative period. Our findings emphasize the importance of identifying patients at high risk for cording, and developing strategies to minimize functional impairment and arm volume elevation associated with cording. Future studies should investigate the effectiveness of interventions for cording following breast cancer treatment.