Appendicitis: This is the most common cause of right iliac fossa pain, especially in young adults. The pain often starts around the navel and then moves to the lower right abdomen. Appendicitis requires prompt medical attention to prevent complications like perforation.

Ovarian Cyst: Ovarian cysts are common in women of reproductive age and can cause pain if they rupture or twist. The pain is usually sharp and can be accompanied by nausea and vomiting.
Ectopic Pregnancy: Although less common, ectopic pregnancy should be considered in any woman of childbearing age presenting with abdominal pain, especially if there's a possibility of pregnancy. The pain can be severe and is often accompanied by vaginal bleeding.
Constipation: Constipation can cause abdominal pain and is more common in women. The pain is often crampy and can be relieved by bowel movements.
Inflammatory Bowel Disease (IBD): Conditions like Crohn's disease and ulcerative colitis can cause chronic abdominal pain, diarrhea, and weight loss. The pain can be in any part of the abdomen but is often in the lower right quadrant.

Ectopic Pregnancy: As mentioned, this is a critical diagnosis to consider due to its high morbidity and mortality if not promptly treated.
Ovarian Torsion: This is a surgical emergency where the ovary twists around its ligaments, cutting off blood supply. It presents with severe, sudden onset pain and requires immediate intervention.
Ruptured Ovarian Cyst: While often not life-threatening, a ruptured ovarian cyst can cause significant pain and internal bleeding, necessitating urgent medical evaluation.
Intestinal Obstruction: This can cause severe abdominal pain, vomiting, and constipation. It requires prompt diagnosis and treatment to prevent complications like bowel ischemia.

Meckel's Diverticulitis: A rare condition where a small bulge in the small intestine (Meckel's diverticulum) becomes inflamed, causing pain, nausea, and vomiting.
Endometriosis: While not rare, endometriosis causing right iliac fossa pain is less common. It's characterized by chronic pelvic pain, dysmenorrhea, and dyspareunia.
Diverticulitis: More common in older adults, diverticulitis can cause left lower quadrant pain but can occasionally present in the right iliac fossa if the diverticula are located in the right colon.
Mesenteric Lymphadenitis: Inflammation of the lymph nodes in the mesentery can mimic appendicitis, causing right lower quadrant pain, often after a viral illness.