Peptic ulcer disease (most common cause)
Gastritis/esophagitis
Gastric/esophageal varices
Mallory-Weiss tear
Malignancy<unk> 
Boerhaave
Dieulafoy's lesion
Angiodysplasia
Hemobilia
Hemorrhagic gastritis, EtOH
Celiac disease
Dengue
Other intrabdominal bleeds
Hemorrhagic pancreatitis
Splenic rupture
Subcapsular cavernous hemangiomas
Peliosis hepatis
Hemorrhagic pancreatitis
Splenic rupture
Subcapsular cavernous hemangiomas
Peliosis hepatis
Hemoptysis
Vaginal/Urethra bleeding
ENT bleeding
Dietary (Iron, bismuth, beets)
Swallowed maternal blood (in neonate)
Upper GI Bleeding
Diverticular disease
Diverticulosis
Diverticulitis
Vascular ectasia / angiodysplasia
Inflammatory bowel disease
Infectious colitis
Mesenteric Ischemia / ischemic colitis
Meckel's diverticulum
Colorectal cancer / polyps
Hemorrhoids
Internal hemorrhoid
External hemorrhoid<unk>  fistula
Nearly 100% mortality if untreated
Consider in patients with gastrointestinal bleeding and known abdominal aortic aneurysms or aortic grafts
Rectal foreign body
Rectal ulcer (HIV, Syphilis, STI)
Anal fissure
Diverticulosis
Diverticulitis
Internal hemorrhoid
External hemorrhoid
Nearly 100% mortality if untreated
Consider in patients with gastrointestinal bleeding and known abdominal aortic aneurysms or aortic grafts
Aortoenteric fisulta
Peptic ulcer disease 
Aortocaval fistula
Gastritis/esophagitis
Intersection syndrome
Gastric/esophageal varices
Angiogram complications
Mallory-Weiss tear