The term ‘T4 syndrome’ is a clinical pattern that involves upper extremity paraesthesia and pain with or without symptoms into the neck and/or head (Maitland, 1986). Mobilization of an upper thoracic vertebrae (commonly T4), reproduces or eliminates these symptoms (Grieve, 1988), although the mechanism for this remains unclear. The presence of a hypomobile thoracic segment may indicate involvement of a synovial joint structure (Bogduk, 1986). However, this is unlikely to somatically refer symptoms to the upper extremity (Grieve, 1988). The sympathetic nervous system may provide a pathway for referral from the thoracic spine to the head and arms, but the link between the sympathetic and the somatic nervous system is not clearly understood (Evans, 1997). The purpose of this case study is to describe a patient who presented with symptoms that closely resembled the clinical condition known as ‘T4 syndrome’. As this syndrome is poorly defined in the literature, this study will detail the history and clinical interpretation of symptoms. This patient responded to thoracic mobilizations and the proposed mechanisms by which thoracic dysfunction are thought to cause upper extremity pain and paraesthesia are discussed.