Gastrointestinal diseases associated with impaired immunity are largely infectious, although an increased incidence of extranodal lymphoma is also found in the context of HIV infection. The range of such infections is related to the role of CD4+ T cells in their eradication. Infections tend to occur with organisms of limited virulence and to be recurrent, and are associated with disseminated infection. The symptoms they produce are usually pain on swallowing, weight loss or diarrhoea. Abdominal pain can be associated with Mycobacterium avium-intracellulare or sclerosis of the bile ducts secondary to infection.