Varying levels of shoulder morbidity following treatment for breast cancer have been reported. Patients report pain, weakness, tightness and reduced functional capacity. Normal painfree motion of the arm and shoulder requires mobility in the scapulothoracic, glenohumeral, acromioclavicular and sternoclavicular joints. Under healthy conditions elevation of the arm is accompanied by scapula retraction, lateral rotation and posterior tilt. However, when scapulothoracic motion is disproportionate to glenohumeral motion, the potential exists for microtrauma and long term pain. A number of studies on women treated for breast cancer have shown limitations in glenohumeral range of movement and a recent report from our laboratory has shown decreased muscle activity in four key muscles acting on the scapula. However, no study has measured the effect of treatment on three-dimensional (3-D) scapulothoracic motion in relation to glenohumeral motion. 152 women treated for unilateral carcinoma of the breast were included in the study. All patients filled out the Shoulder Pain and Disability Index (SPADI). 3-D-kinematic data for the humerus and scapula was recorded during scaption on the affected and unaffected side. The association between kinematic data, SPADI and covariates was determined using random effects multiple regression techniques. All scapula kinematic parameters were significantly altered on the side of the carcinoma in breast cancer survivors. Both reported levels of pain and dysfunction were associated with altered kinematics. High levels of pain and disability were reported for up to 6 years post surgery. Patients with the left side affected reported higher levels of pain and demonstrated more significant scapulathoracic dysfunction independent of dominance. Altered movement patterns were different for left versus right side affected. Left side affected patients need to be considered as a group of patients at risk of experiencing higher levels of pain and showing greater shoulder dysfunction. Whether cause or effect, pain reports are accompanied by 3-dimensional scapula dysfunction which mimics that of many other shoulder conditions.