Porto-spleno-mesenteric vein thrombosis is a rare, life-threatening condition of extrahepatic portal venous system thrombosis. We report a rare case of a 49-year-old lady with late presentation of acute portal vein thrombosis in a non-cirrhotic liver with an incidental finding of left adnexal teratoma. She presented with a one-week history of severe abdominal pain associated with vomiting and diarrhea. She gave no history of prior risk for venous thromboembolism or liver diseases. Physical examination revealed a tender mass extending from suprapubic to left iliac fossa. Abdominal computed tomography scans showed a well-defined fat-containing left adnexal mass, likely a benign teratoma, with no involvement of surrounding structures or calcification. There was evidence of porto-splenic-mesenteric vein thrombosis with liver infarction, bowel and splenic ischemia. Management of the extensive thrombosis causing multi-organ failure includes resuscitation, supportive care and treatment of thrombosis. Treatment options include early anticoagulation and if feasible, thrombolysis.