A 50-year-old severely immunodeficient woman with malignant non-Hodgkin lymphoma died from graft-versus-host disease due to transfusion of a single unit of packed red cells. Three days after this transfusion a maculo-papular rash appeared, followed by generalized erythroderma refractory to therapy and eventually progressing into generalized ulcero-squamous dermatitis. This case, and a review of other similar cases published elsewhere, prompt the authors to recommend prophylactic irradiation of blood products prior to their administration to patients with cellular immunodeficiency, particularly in cases of acute leukaemia or malignant lymphoma where patients receive intensive radio- and/or chemotherapy regimens. To appreciate the degree of cellular immunodeficiency in such risk patients, simple criteria should be developed to assess the efficiency of the cellular immune system.