If there is pain under the rib cage in the right upper abdomen, diseases of the hepatobiliary system need to be considered. Liver diseases, including fatty liver, liver tumors, and cholestatic liver disease, can cause the patient’s liver to increase in size, pulling on the peritoneum of the liver surface and causing abdominal distension and pain. Diseases of the gallbladder system can also manifest as vague pain in the patient’s right upper abdomen, including conditions such as acute cholecystitis, chronic cholecystitis, and gallbladder tumors. Gallbladder stones are an important cause of the onset of cholecystitis, and patients may feel pain in the right upper abdomen if there is stone impaction, or if the gallbladder duct causes bile stasis and gallbladder distention. If there is a combination of bacterial infection causing acute cholecystitis, the patient will experience more intense right upper abdominal pain along with nausea, vomiting, fever, and jaundice.