Portal vein thrombosis usually appears in the course of acute abdominal septic complications or after splenectomy, though in 50% of cases no aetiological factors can be identified. In our department we recently treated two patients affected by portal vein thrombosis, the first after splenectomy for haematological disease, and the second after sigmoid diverticulitis. When portal vein thrombosis occurs after splenectomy for haematological reasons, the increased viscosity of the blood due to thrombocytosis is the main factor regarded as being the cause. In the first case, acute abdominal pain appeared 15 days after splenectomy and the diagnosis was suspected and confirmed by Doppler ultrasonography. The clinical course in the second case was less typical, because, although the sigmoid diverticular disease was known, the symptomatology presented with high fever but no clear subjective or objective abdominal picture. The diagnosis was achieved by computed tomography. The clinical picture may vary greatly but usually abdominal pain, fever and intestinal ischaemia are present. Nowadays the diagnosis has improved as a result of the extensive use of Doppler ultrasonography and computed tomography. Fibrinolytic therapy and acetylsalicylic acid are the treatment of choice and in our experience the clinical picture tends to clear up rapidly. When the patient presents a number of risk factors, prophylaxis of portal vein thrombosis should be planned.