The gastrointestinal manifestations of AIDS in children are related to opportunistic infections, lymphoproliferative disease, and cancer. The infections that affect the gastrointestinal tract at different sites also occur in patients without AIDS. However, in children with AIDS, the infections are more severe, often relapse, and are harder to eradicate. Candidiasis is the most common infection in the esophagus, but infections caused by herpes simplex virus and cytomegalovirus also are common. Radiologic findings include ulcerations, a cobblestone appearance, and disordered motility. Gastritis and enteritis are usually caused by cytomegalovirus. Lesions produced by this virus include ulcerations caused by ischemic necrosis as a result of vasculitis. Barium studies show increased nodularity and effacement of mucosa. Other organisms (typically found in all immunocompromised patients) include Mycobacterium avium-intracellulare, Mycobacterium tuberculosis, Campylobacter, Giardia, and Cryptosporidium. Colitis and proctitis are caused by many of the same enteric pathogens. Cytomegalovirus is the most virulent, causing necrosis, perforation, and often death. Lymphoma, smooth muscle tumors, and Kaposi's sarcoma are the most common neoplasms encountered in children with AIDS.