Reactivation of chronic Chagas' disease is a rare condition and occurs only in immunosuppressed patients. We report a case of a patient with a rapid and fatal reactivation of Chagas' disease, manifested by meningoencephalitis, which lead to a diagnosis of acquired immunodeficiency syndrome (AIDS). We believe there is sufficient evidence to include the reactivation of Chagas' disease among the diagnostic criteria of AIDS in Human Immunodeficiency Virus (HIV) infection.