A 79-year-old male patient presented to our hospital with chief complaints of fever, abdominal pain, and jaundice. Laboratory data revealed marked hepatobiliary enzyme and inflammatory marker elevations, and computed tomography revealed ascending colon diverticulitis, thrombophlebitis, portal vein thrombus, and intrahepatic cholangitis. Blood culture revealed the presence of Prevotella sp. The patient was treated with anticoagulant therapy in addition to antimicrobial therapy;however, activated partial thromboplastin time prolongation remained insufficient. Antithrombin therapy was combined with the current therapy because antithrombin levels were low, which resulted in iliopsoas muscle hematoma. The hematoma resolved conservatively after discontinuing anticoagulation, and the patient was discharged after 19 days of hospitalization with improved cholangitis and diverticulitis. The portal vein thrombus remained after discharge;however, anticoagulation therapy was not restarted due to adverse events. This case was presented because of its difficult treatment.