Over l0 million endoscopies and surgical procedures involving the GI tract are performed each year. Community-based studies from around the world demonstrate that 10% to 46% of all children meet the criteria for RAP. Gastrointestinal disorders such as chronic or acute diarrhea, malabsorption, abdominal pain, and inflammatory bowel diseases can indicate immune deficiency, present in 5% to 50% of patients with primary immunodeficiencies. The gastrointestinal tract is the largest lymphoid organ in the body, so it is not surprising that intestinal diseases are common among immunodeficient patients. Gastroenterologists therefore must be able to diagnose and treat patients with primary immunodeficiency. Further, pathogens do influence the gut function. On the other hand, dietary habits and specific food types can play a significant role in the onset, treatment, and prevention of many GI disorders. Many of these can be prevented or minimized by maintaining a healthy lifestyle, and practicing good bowel habits.