We report a case of Burkitt's lymphoma developing in a 7-year-old boy with hyper-IgE syndrome. This is the third reported case of malignancy in the hyper-IgE syndrome. The other two cases were an 18-year-old man with Hodgkin's disease and a 10-year-old girl with histiocytic lymphoma. The patient developed retroperitoneal Burkitt's lymphoma with probable metastasis to the brain. His short life was characterized by recurrent staphylococcal skin, middle ear, and lung infections associated with extremely elevated serum concentrations of IgE. There was also an associated disturbance of bone metabolism with osteoporosis and pathologic fractures and absence of parathormone, findings that have been observed in other patients with hyper-IgE syndrome and other forms of T cell immunodeficiency. At the age of 5 years, inadequate B cell responses to immunization with antigens derived from diphtheria, tetanus, and Haemophilus influenzae type b organisms and with the OX174 bacteriophage were demonstrated in the patient. In his terminal state his in vitro lymphocyte analysis demonstrated findings of anergy. Although the precise immunologic defect in hyper-IgE syndrome is unknown, these cases of associated malignancy stress the role that a completely normal immune system plays in preventing the premature appearance of cancer.