Appendicitis: This is often the first consideration for right-sided abdominal pain, especially if the pain is localized to the right lower quadrant. The classic presentation includes initial diffuse or periumbilical pain that migrates to the right lower quadrant, accompanied by fever, nausea, and vomiting.

Gallbladder Disease (Cholecystitis or Cholelithiasis): Right upper quadrant pain, especially after eating fatty foods, suggests gallbladder pathology. Symptoms can include pain, jaundice, and fever.
Kidney Stones (Nephrolithiasis): Severe, colicky pain that radiates from the flank to the groin, often accompanied by nausea, vomiting, and hematuria, points towards a kidney stone.
Diverticulitis: While more common on the left, diverticulitis can occur on the right side, presenting with pain, changes in bowel habits, and possible fever.
Inflammatory Bowel Disease (Crohn's Disease or Ulcerative Colitis): Chronic abdominal pain, diarrhea, weight loss, and sometimes blood in stool can indicate IBD, which can affect any part of the gastrointestinal tract.

Ectopic Pregnancy: In women of childbearing age, a missed ectopic pregnancy can be fatal. Symptoms include severe abdominal pain, vaginal bleeding, and a positive pregnancy test.
Ruptured Aortic Aneurysm: Although more central, a ruptured abdominal aortic aneurysm can present with severe abdominal or back pain and is immediately life-threatening.
Ovarian Torsion: Sudden, severe pelvic pain, often with nausea and vomiting, can indicate ovarian torsion, which requires immediate surgical intervention.
Intestinal Obstruction: Symptoms like severe abdominal pain, vomiting, obstipation, and abdominal distension suggest an obstruction, which can lead to ischemia and necrosis if not promptly addressed.

Hepatic Abscess or Infarct: Right upper quadrant pain with fever and jaundice could suggest a liver abscess or infarct, especially in patients with underlying liver disease or risk factors for embolic events.
Right-Sided Pneumonia: Basilar pneumonias can cause referred abdominal pain, especially if the diaphragm is involved.
Pancreatitis: Although more commonly associated with central abdominal pain, pancreatitis can present with right upper quadrant pain, especially if the head of the pancreas is involved.
Mesenteric Ischemia: Severe, diffuse abdominal pain out of proportion to physical examination findings, especially in older patients or those with risk factors for embolic events, should raise suspicion for mesenteric ischemia.