Acute and chronic graft-versus-host disease (GVHD) are significant complications of allogeneic bone marrow transplantation that occur when immunologically active T-cell lymphocytes are transplanted into an immunosuppressed recipient who is genetically disparate from the marrow donor. Oral GVHD lesions closely resemble those seen with a number of autoimmune connective tissue disease, including lichen planus, systemic sclerosis, lupus erythematosus, and Sjögren's syndrome. Mucosal erythema, atrophy, and ulceration are noted clinically; lichen planus-like lesions are the most distinctive oral lesions. Salivary gland changes include changes in both flow rate and sialochemistry. Oral involvement ranges between 33% and 75% for patients with acute GVHD and upwards of 80% for those with chronic GVHD. Management of oral GVHD lesions depends on successful systemic therapy, although topical steroids can be of help in some instances.