Polyarteritis nodosa (PAN) is a necrotizing, focal segmental vasculitis that affects predominantly medium-sized arteries in many different organ systems. It is associated with hepatitis B virus (HBV) in about 7% of cases, a decline from about 30% before the mandatory testing of blood products and the widespread vaccination programs. HBV PAN is an early postinfectious process. The hepatitis is silent in most cases, with mild transaminase level increases in 50% of patients. Gastrointestinal involvement occurs in 14% to 65% of patients with PAN. Postprandial abdominal pain from ischemia is the most common symptom. When transmural ischemia develops, there may be necrosis of the bowel wall with perforation, associated with a poor prognosis. Liver involvement occurs in 16% to 56% of patients, although clinical manifestations related to liver disease are quite rare. Acalculous gangrenous cholecystitis may develop owing to arteritis involving the wall of the gallbladder. Microaneurysms on arteriography or computed tomography angiography are characteristic of PAN, but are seen in other conditions. Tissue biopsy may confirm the diagnosis, although involvement is segmental. Corticosteroids are used for non-HBV PAN with cyclophosphamide added for severe disease. For PAN related to HBV, a 2-week course of corticosteroids is begun, with plasma exchanges and an antiviral agent. Corticosteroids and cyclophosphamide have improved patient outcome so that the 1-year survival rate is now about 85%.