The occurrence of chylothorax due to thrombosis of the subclavicular venous drainage is reported. This occurred in a young adult with previously undiagnosed Behçet's disease which had been developing over three years. Venous thromboses during the course of Behçet's disease are extremely frequent and are currently one of the diagnostic criteria. When these thromboses involve the central veins, in particularly the superior vena cava or one of its branches a chylothorax is possible due to blockage of the lymphatic circulation and may be a grave complication, given its location.