Acute oral problems that frequently occur during oncologic therapy include mucositis, infection, and hemorrhage. Certain chemotherapeutic agents consistently produce significant mucositis. Herpes simplex virus infection is a frequent cause of oral ulceration. Gram-negative oral bacilli can cause severe local necrosis of oral tissues and lethal bacteremia and sepsis. Sepsis with oral streptococci is common in the early postengraftment period following bone marrow transplant. A case report describes the successful use of a new hemostatic agent to control hemorrhage in a patient with severe thrombocytopenia in leukemic relapse. Long-term dental complications of oncologic therapy include abnormal dental and craniofacial development. Dental abnormalities in children treated for acute lymphoblastic leukemia are more severe if oncologic therapy begins before 5 years of age and if cranial irradiation is used. The combination of high-dose cranial irradiation (2400 cGy) and chemotherapy before 5 years of age results in deficient mandibular growth. In children with reduced growth hormone production and deficient mandibular growth due to treatment with bone marrow transplantation, stimulation of mandibular condylar growth is reported following the use of growth hormone.