For the acute abdomen, chest X-ray is essential because:-For small pneumoperitoneum, chest x-ray in an upright position (erect) is best. A number of chest conditions may present as an acute abdominal pain (e.g. lower lobe pneumonia, MI). The acute abdominal condition may be complicated by chest pathology, e.g. pleural effusion frequently complicates acute pancreatitis. Even when chest radiograph is normal it acts as a valuable baseline.