Gallbladder disease (cholecystitis or cholelithiasis): This is often the most common cause of acute right upper quadrant pain, especially in females and individuals with a history of gallstones. The pain is typically sharp and may radiate to the right shoulder.

Peptic ulcer disease: Both gastric and duodenal ulcers can cause right upper quadrant pain, especially if the ulcer is located in the duodenum or if there is associated inflammation of the surrounding tissues.
Hepatitis: Viral or alcoholic hepatitis can cause right upper quadrant pain due to liver inflammation.
Right lower lobe pneumonia: Sometimes, pneumonia in the right lower lobe can cause referred pain to the right upper quadrant due to the proximity of the diaphragm to the lung.

Appendicitis (with an atypical presentation): Although appendicitis typically presents with right lower quadrant pain, an inflamed appendix can sometimes be located in a retrocecal position, causing pain in the right upper quadrant.
Myocardial infarction: A heart attack can cause referred pain to the right upper quadrant, especially if the inferior wall of the heart is involved.
Pulmonary embolism: A large pulmonary embolism can cause sudden onset of chest pain that may be referred to the right upper quadrant.
Aortic dissection: This is a life-threatening condition where the inner layer of the aorta tears, causing severe pain that can be referred to various parts of the body, including the right upper quadrant.

Fitz-Hugh-Curtis syndrome: A rare condition where pelvic inflammatory disease causes inflammation of the liver capsule, leading to right upper quadrant pain.
Hepatic artery aneurysm: A rare condition where an aneurysm of the hepatic artery can cause right upper quadrant pain due to rupture or thrombosis.
Right upper quadrant tumor: Tumors of the liver, gallbladder, or bile ducts can cause pain in the right upper quadrant, although this is less common than other causes.