Question: what is the most common gastrointestinal disease?
Answer: Gastroesophageal Reflux Disease (GERD) Heartburn happens, but if it occurs regularly, you may need to be evaluated for GERD. ... 
Chronic Diarrhea. ... 
Chronic Constipation. ... 
Gastroenteritis. ... 
Ulcers. ... 
Hemorrhoids.