Nephrolithiasis (Kidney Stones): This is often the first consideration for flank pain, especially if the pain is severe and radiates to the groin. The right flank is a common location for pain due to the anatomy of the urinary tract.

Pyelonephritis: An infection of the kidney, which can cause flank pain, fever, and other urinary symptoms. It's a common cause of flank pain, especially in women.
Musculoskeletal Strain: Given the location, strain or injury to the muscles in the flank area can mimic more serious conditions and is relatively common.
Urinary Tract Infection (UTI): While often causing more lower urinary tract symptoms, a UTI can sometimes present with flank pain, especially if it's ascending.

Appendicitis: Although appendicitis typically presents with right lower quadrant pain, it can occasionally cause right flank pain if the appendix is retrocecal. Missing this diagnosis can lead to severe consequences.
Pulmonary Embolism: Can cause sudden onset of flank pain if the embolism affects the pulmonary vessels near the diaphragm, though this is less common.
Aortic Dissection: A life-threatening condition that can cause severe flank pain among other symptoms. It's crucial to consider this in patients with risk factors like hypertension.
Ectopic Pregnancy: In women of childbearing age, ectopic pregnancy can cause flank pain and is a medical emergency.

Pheochromocytoma: A rare tumor of the adrenal gland that can cause episodic hypertension and flank pain.
Renal Cell Carcinoma: A type of kidney cancer that might cause flank pain, though it's more commonly associated with hematuria.
Retroperitoneal Fibrosis: A rare condition characterized by the proliferation of fibrous tissue in the retroperitoneum, which can encase and obstruct structures like the ureters, leading to flank pain.