The infected and inflamed periodontium can act as a focus for systemic infection in neutropenic cancer patients. The incidence of these oral infections is unknown, but probably underestimated. Periodontal infections can easily be overlooked, primarily because symptoms of gingival inflammation may be minimal and the infection may be located in deeper parts of the periodontium. Assessment of a patient's periodontal condition before the onset of profound neutropenia is critical to the diagnosis and the management of these potentially life-threatening infections. This review article is aimed at informing supportive care providers of recent insights into the pathogenesis of periodontal diseases and the role of subgingival microorganisms, with the emphasis on these infections in cancer patients treated with high-dose chemotherapy. Furthermore, a multidisciplinary approach to the management of periodontal infections and the need for future research is discussed.