Central venous thrombosis is an uncommon problem associated with malignancy. We present here a 53- year-old male who visited the emergency room because of right neck swelling. Fluid accumulation over deep neck space led to the diagnosis of suspected hemorrhage, and central venous thrombosis was found by computed tomography. This patient had no other precipitating cause. Autoimmune disorders, hypercoagulation and malignancy surveys were performed during hospitalization. Elevated serum tissue polypeptide antigen and CA130 were noted, and multiple liver metastases were found by another computed tomography. Subsequently, gastric adenocarcinoma was confirmed after gastroendoscopy. Gastric adenocarcinoma with distal metastases was finally diagnosed. This case reminds us that central venous thrombosis is a sign of many diseases. Malignancy, including gastric adenocarcinoma, is one of the causes that should be considered.