A 49-year-old, previously healthy woman sought treatment for abdominal pain. Colonoscopy revealed ascending colon cancer. Computed tomography and angiography showed splenic metastasis and thrombosis extending from the splenic vein to the portal vein. She underwent right hemicolectomy, splenectomy, and distal pancreatomy. Histological findings showed no malignant cell in the splenic vein which was filled with organizing thrombus. We postulate the mechanism of splenic vein thrombosis in our case to be secondary to the extrinsic compression of the splenic vein by the splenic metastasis or by the inflammatory process produced by the splenic metastasis. In conclusion, we suggest that splenic metastasis should be added to the list of differential diagnosis which causes splenic vein thrombosis. In the absence of other sites of neoplastic disease, splenectomy seems to be the preferred therapy because it can be performed with low morbidity and harbors the potential for long-term survival.