A 1-year-old boy with Wiskott-Aldrich Syndrome (WAS) who developed malignant lymphoma is described. He showed various complications such as atypical lymphocytosis, disseminated intravascular coagulation (DIC), intracranial hemorrhage, macroamylasemia, and monoclonal gammopathy (immunoglobulin A kappa chain). Epstein-Barr virus (EBV) DNA was detected in the tumor tissue, and the monoclonality of B cells from the tumor tissue was established. EBV-associated lymphoma is frequently observed in immunocompromised patients including those with WAS. The development of macroamylasemia, which is rare in childhood, is discussed in relation to lymphoma and monoclonal gammopathy. This case is unique in that the EBV-associated malignant lymphoma developed at an early age and was accompanied by macroamylasemia.