Constipation: This is often the most common cause of a distended abdomen, especially in the elderly or those with a history of bowel habits that are not regular. Constipation leads to the accumulation of feces in the intestines, causing abdominal distension.

Ascites: The accumulation of fluid in the peritoneal cavity, often due to liver cirrhosis, can cause significant abdominal distension. Other causes include heart failure, kidney disease, and certain cancers.
Obstruction of the intestine: Either mechanical (due to adhesions, hernias, or tumors) or functional (due to conditions like paralytic ileus), intestinal obstruction prevents the normal movement of intestinal contents, leading to distension.
Inflammatory bowel disease (IBD): Conditions like Crohn's disease and ulcerative colitis can cause chronic inflammation and distension of the abdomen due to the accumulation of gas and fluid.

Ovarian torsion: Although less common, ovarian torsion is a surgical emergency that can present with sudden onset of abdominal distension, among other symptoms. It requires immediate attention to preserve the ovary.
Ruptured abdominal aortic aneurysm: A life-threatening condition where the aorta ruptures, leading to severe abdominal pain and potentially distension due to internal bleeding.
Perforated viscus: A hole in the wall of the stomach or intestine can lead to peritonitis, an infection of the abdominal cavity, which may cause distension along with severe pain and tenderness.

Lymphoma: Certain types of lymphoma can cause abdominal distension due to the accumulation of lymphatic fluid or the growth of tumors in the abdomen.
Cystic fibrosis: In advanced cases, cystic fibrosis can lead to distal intestinal obstruction syndrome (DIOS), causing abdominal distension.
Abdominal tuberculosis: A rare condition in many parts of the world, abdominal tuberculosis can cause ascites, intestinal obstruction, and abdominal distension among other symptoms.