The gastrointestinal tract plays an important role in the nutritional and immunologic status of human immunodeficiency virus (HIV)-infected individuals. Defective mucosal immunoregulation contributes to the development of bacterial, viral, fungal, or protozoal opportunistic infections. Malabsorption also may occur without an identifiable enteric pathogen. HIV-infected children become lactose intolerant earlier than would be predicted by age or nationality. Although the mechanism is unknown, the mucosal immune system may regulate epithelial cell function through production of cytokines. The role of HIV in the production of cytokines and the relationship to malabsorption remains to be determined. The hypothesis that malabsorption and infection are exacerbated by malnutrition and potentiated by immunodeficiency may lead to the development of effective strategies for nutritional intervention. This has particular relevance for the HIV-infected child.