Enchondroma of the first rib is a rare cause of Thoracic Outlet Syndrome (TOS) manifested by deep venous thrombosis (DVT). Diagnostic difficulties and therapeutic options are discussed. DVT of the upper limb represent 2%-4% of all DVT and are divided into primary and secondary. Venous compression represents 8% of TOS and generally results from a narrowing of the costo-clavicular space. A post-thrombotic syndrome (PTS) is found in 40%-80% despite anticoagulation and rest. However following local infusion of thrombolytic agents only 10% of the subjects develop PTS. Follow-up studies reveal a complete recanalisation of the vein in 45% of the patients treated with thrombolysis, whereas it occurs in only 4% under anticoagulation alone. This favourable result is obtained at the cost of an increased risk of hemorrhagic complications (5%). The solitary enchondroma is a benign cartilaginous tumor preferentially localised in the extremities, hands and feet. A review of the literature reveals that a total of 40 cases of enchondromas have been reported so far, among which 18 were localised in the first rib. The proximity of the neuro-vascular elements and a possible malignant transformation in 2% of the cases justify the ablation of the tumor. Thrombolysis is still highly controversial but gives the best long term prognosis in young patients.