AbstractAtaxia telangiectasia is agenetically determined immunodeficiency with predisposition to malignancy. Herein we report a case of ataxia telangiectasis in a child who had showed high antibody titers to viral capsid antigen (VCA), presence of antibodies to Epstein‐Barr virus (EBV) induced early antigen (EA), low titers of antibodies to EBV associated nuclear antigen (EBNA), and a high incidence of EBNA‐positive cells in the peripheral blood without symptoms of infectious mononucleosis before succumbing to malignant lymphoma five years later. We hypothesize the association betwen some cytogenetic defects and persistent EBV infection on the development of the malignant lymphoma in this pati