Oral mucosal ulceration is a frequent complication in bone marrow transplantation, resulting from epithelial injury caused by cytotoxic chemotherapy and radiation conditioning, as well as from pre-existing infection. Oral mucositis causes pain, interferes with patient nutrition, and can lead to systemic infection and other complications that increase patient morbidity and mortality; this complication also markedly increases the expense of bone marrow transplantation. A variety of interventions have been assessed for preventing oral mucositis or reducing the severity of mucositis and its sequelae. These include meticulous pretransplantation and ongoing mouth care, calcium phosphate solution, near-infrared light and lower-energy laser treatment, interleukin-11, sucralfate, oral glutamine, granulocyte-macrophage colony-stimulating factor rinse, tretinoin, and keratinocyte growth factor; particularly promising results have been observed with use of the cytoprotectant/radioprotectant agent amifostine. Reduction in the severity and duration of oral mucositis and its sequelae in patients undergoing bone marrow transplantation can have a substantial impact on morbidity and mortality and cost of care. Further systematic evaluation of approaches to prevention and management of oral mucositis is necessary to define optimal strategies in the transplantation setting.