Appendicitis: This is the most common cause of right lower quadrant (RLQ) abdominal pain, especially in younger individuals. The pain often starts around the navel and then moves to the RLQ. Appendicitis requires prompt surgical intervention to prevent rupture.

Ovarian Cyst or Torsion: In females, ovarian cysts can cause RLQ pain, especially if they rupture or torsion occurs. The pain can be severe and is often accompanied by nausea and vomiting.
Ectopic Pregnancy: Another consideration in females, ectopic pregnancy can present with RLQ pain, vaginal bleeding, and symptoms of early pregnancy.
Diverticulitis: Although more common on the left side, diverticulitis can occur on the right and cause RLQ pain, especially in individuals with right-sided diverticula.
Intestinal Obstruction: Obstruction of the small or large intestine can cause abdominal pain that may be localized to the RLQ, depending on the site of obstruction.
Inflammatory Bowel Disease (IBD): Conditions like Crohn's disease or ulcerative colitis can cause chronic or acute abdominal pain, including in the RLQ, along with changes in bowel habits and possibly weight loss.

Ectopic Pregnancy: As mentioned, this is a critical diagnosis to consider in any female of childbearing age presenting with RLQ pain, due to its high morbidity and mortality if not promptly treated.
Ruptured Aneurysm or Aortic Dissection: Although these conditions typically present with back or abdominal pain that may not be limited to the RLQ, they are life-threatening emergencies that require immediate diagnosis and treatment.
Ovarian Torsion: This condition can lead to necrosis of the ovary if not promptly treated, making it a critical diagnosis not to miss in females with RLQ pain.
Mesenteric Ischemia: This condition, involving insufficient blood flow to the intestines, can present with severe abdominal pain and is a surgical emergency.

Meckel's Diverticulitis: A congenital anomaly of the small intestine, Meckel's diverticulum can become inflamed and cause RLQ pain, mimicking appendicitis.
Carcinoid Tumor: These rare tumors can occur in the appendix or small intestine and may cause abdominal pain, among other symptoms.
Intussusception: A condition where a part of the intestine slides into an adjacent part, intussusception can cause intermittent abdominal pain, including in the RLQ, and is more common in children.
Right-sided Diverticulitis: While diverticulitis is more common on the left, right-sided diverticulitis can occur and cause RLQ pain, especially in individuals with right-sided diverticula.