A 33-year-old man with no history of interest and no known family history of thrombosis came to the emergency department for intermittent diffuse abdominal pain of several days' evolution with nausea and some alimentary vomiting. Physical examination revealed diffuse pain on abdominal palpation with no signs of peritoneal irritation. The most relevant analytical data were: glucose 84 mg/dl, urea 30 mg/dl, creatinine 0.9 mg/dl, amylase 29 U/l, lactate dehydrogenase 241 U/l, aspartate aminotransferase 26 U/l, total bilirubin 0.9 mg/dl, C-reactive protein 4.1 mg/dl, haemoglobin 14.4 mg/dl, platelets 301. 000 mm3, leukocytes 6,700 mm3, prothrombin activity 85%, fibrinogen 518 mg/dl and D-dimer 5,871 ng/ml. An abdominal ultrasound showed an enlarged portal vein (1.6 cm in diameter), with no flow within it on Doppler study. An abdominal CT scan showed thrombosis of the portal vein and superior mesenteric vein, with no other alterations. The patient was treated with enoxaparin (1 mg/kg every 12 hours) for 10 days, with a favourable evolution, and then continued treatment with acenocoumarol. The thrombophilia study identified heterozygosity for the G20210A mutation of the prothrombin gene, with factor V Leiden, activated protein C resistance, lupus anticoagulant, IgG and IgM anticardiolipin antibodies, proteins C and S, antithrombin and plasma homocysteine being normal or negative. An MRI angiogram performed 10 months later showed a 15 cm splenomegaly and an enlarged but patent portal vein with cavernomatous transformation (with small periportal collateral vessels). An oral gastrointestinal endoscopy performed 14 months after the initial picture was normal. After 15 months of follow-up treatment with acenocoumarol, the patient remains asymptomatic.