The most common cause of pain under the right posterior rib cage is pleurisy. Inflammation of the right pleura can cause symptoms of pain under the right posterior rib cage, which can worsen with breathing or coughing. Then there is localized costochondritis or intercostal neuralgia, while lesions of the ribs themselves, such as rib fractures, rib cartilage fractures, and bone contusions, can also cause symptoms of right posterior subcostal pain. Local muscle damage, such as prolonged ambulatory work or improper sitting and twisting of the back, and improper sleeping posture, can damage the muscles, and local muscle damage can lead to pain under the right posterior rib cage. Inflammation of the right side of the lung and liver lesions can also cause pain under the right posterior rib cage, and liver lesions such as liver abscess, hepatitis and liver cancer can also cause pain under the right posterior rib cage. Therefore, if you experience pain under the right posterior rib cage, go to the hospital and have an examination done under the guidance of your doctor to see what is causing it.