An 8-year-old male underwent excision of an encapsulated thymoma. Four months later he presented with disseminated, fatal varicella. Evaluation of his immune status during the terminal illness revealed hypogammaglobulinemia and lymphopenia consistent with a diagnosis of Good's syndrome (immunodeficiency with thymoma). This is the first case of Good's syndrome reported in a child and the first case of fatal varicella associated with Good's syndrome. The combination of this rare pediatric tumor and immunodeficiency is discussed. Despite specific antiviral therapy, varicella remains a deadly disease in the immunocompromised host.