Immunological competence and nutritional status are two of the most important determinants of morbidity and mortality. Oral diseases, particularly inflammatory periodontal lesions, are caused by viruses and specific periodontopathic bacteria. Paradoxically, the production of cytokines and oxidant molecules, which are supposed to be part of a highly effective mechanism for combating the periodontal pathogens, may damage the host. Malnutrition consistently impairs innate and adaptive defenses of the host, including phagocytic function, cell-mediated immunity, complement system, secretory antibody, and cytokine production and function. In protein-energy malnutrition, there are marked changes in the oral microbial ecology resulting in a preponderance of pathogenic anaerobic organisms, increased propensity of bacteria to bind to oral mucosal cells, attenuation of acute phase protein response, and dysfunction of the cytokine system. Cellular depletion of antioxidant nutrients promotes immunosuppression, accelerated replication rate of ribonucleic acid viruses, and increased disease progression. Therefore, malnutrition can intensify the severity of oral infections and may lead to their evolution into life-threatening diseases.