Primary spontaneous upper extremity deep vein thrombosis is characterised by thrombosis within deep veins draining the upper extremity due to anatomical abnormalities of the thoracic outlet causing axillosubclavian compression and subsequent thrombosis. It is an uncommon condition that typically presents with unilateral arm swelling in a young male following vigorous upper extremity activity. The diagnosis of this condition is usually made by Doppler ultrasound, but other investigations are mandatory to exclude the secondary causes of upper extremity DVT. Different treatment options are available including anticoagulation, thrombolysis, and surgery. We report the case of a young healthy male with athletic physique who presented with pain and swelling of his dominant arm after weightlifting in the gym.