Bone marrow transplantation (BMT) is the treatment of choice for many leukemias, lymphomas, bone marrow failure syndromes, and immunodeficiency disorders, and is the primary and salvage therapy for many solid malignancies. With the establishment of national and international marrow banks, unrelated allogeneic BMT is being performed with increasing frequency. Graft-vs.-host disease (GVHD) remains a major complication of allogeneic BMT, occurring in 25% to 70% of patients despite GVHD prophylaxis, with the skin, gastro-intestinal tract, and liver as primary target organs. Oral findings are seen in both acute and chronic GVHD. In acute GVHD, the oral lesions are often painful, erythematous, ulcerative, and desquamative. In chronic GVHD, they are lichenoid with associated erythema and ulcerations; additionally, they may be associated with a sicca syndrome characterized by xerostomia and progressive salivary gland atrophy. General principles of BMT are discussed, as are systemic and local therapeutic options for oral GVHD.