Post-transplantation lymphoproliferative disorders (PTLD) represent a severe complication of organ transplantation, so the determination of prognostic factors for the response and the survival is of major interest. Studies on PTLD are hindered by the small number of cases, explaining the conflicting published results. In order to identify, prognostic factors in this kind of disease, 61 patients have been analyzed in a retrospective multicenter study. A new index is proposed to assess the survival probability, it is composed of two factors: the performance status (PS < or = 1 versus 2-3) and the number of involved sites (1 versus > 1). This index seems to be more accurate in PTLD than the IPI, the reference in immunocompetent patients with non Hodgkin lymphomas. However, a similar analysis in a more homogeneous population remains necessary.