Effort thrombosis of the upper extremity is secondary to thrombosis of the axillary and/or subclavian veins that develop from heavy arm exertion. This case illustrates venous thrombosis of the right brachiocephalic vein in a 32-year-old man who presented with a cyst-like swelling in the right neck with no associated pain or trauma. Our patient, a trained athlete, was preparing for a triathlon at the time of presentation. He was treated by first-line therapy of subcutaneous and oral anti-coagulation medication. In this study, we highlight the importance of early investigation and treatment of symptomatic athletes so that long-term disability can be prevented. This study also shows the timely use of computed tomography imaging, which can help to identify the syndrome in previously undiagnosed patients.