A 35-year-old previously healthy man developed a painful swelling in the area of the left sternoclavicular joint (SCJ), restricting movement. There had been no history of trauma.A moderately increased erythrocyte sedimentation rate was the only abnormal finding among the usual laboratory tests. Radiologically there were marked hyperostotic changes in the area of the left upper thoracic cage with synostosis of the SCJ. Biopsy of the left clavicle showed non-specific chronic sclerosing osteomyelitis.Over the next 6 years the SCJ became completely ankylosed and there were now extensive fibroses, some presternal and some in the upper mediastinum with thrombosis of the left subclavian, axillary and jugular veins causing inflow occlusion (Paget-von-Schroetter-syndrome). Lymph nodes in the region of the mandible, jugular veins bilaterally and mediastinum were noted for the first time, remaining unchanged in size over six months.Sternoclavicular hyperostosis is an important condition in the differential diagnosis of inflammatory or malignant processes of this joint.