In Epstein-Barr virus (EBV) negative Hodgkin's cell lines and classical EBV-negative Hodgkin's lymphoma (HL), ReedSternberg cells (RS cells) represent end-stage tumor cells, in which further nuclear division becomes impossible because of sustained telomere loss, shortening and aggregation. However, the three-dimensional (3D) telomere organization in latent membrane protein 1 (LMP1)-expressing RS cells of EBV-associated HL is not known. We performed a 3D telomere analysis after quantitative fluorescent in situ hybridization on 5 mm tissue sections on two LMP1-expressing HL cases and showed highly significant telomere shortening (Po0.0001) and formation of telomere aggregates in RS cells (Po0.0001), when compared with the mononuclear precursor Hodgkin cells (H cells). Telomere-poor or telomere-free 'ghost' nuclei were a regular finding in these RS cells. These nuclei and their telomere content strongly contrasted with the corona of surrounding lymphocytes showing numerous midsized telomere hybridization signals. Both H cells and RS cells of two EBV-negative HL cases analyzed in parallel showed 3D telomere patterns identical to those of LMP1-expressing cases. As a major advance, our 3D nuclear imaging approach allows the visualization of hitherto unknown profound changes in the 3D nuclear telomere organization associated with the transition from LMP1-positive H cells to LMP1-positive RS cells. We conclude that RS cells irrespective of LMP1 expression are end-stage tumor cells in which the extent of their inability to divide further is proportional to the increase of very short telomeres, telomere loss, aggregate formation and the generation of 'ghost' nuclei. Mononuclear H cells are the precursors of multinuclear RS cells, 6-9 and endomitotic multinucleation is associated with disturbed cytokinesis and jumping translocations 10,11 pointing to a severe telomere dysfunction. 12,13 Telomeres are the nucleoprotein complexes at the ends of chromosomes in which a number of specific proteins, either binding telomere proteins directly or a protein complex, termed 'shelterin,' is directly associated with telomeric DNA. [14][15][16] Profound changes in the three-dimensional (3D) nuclear organization of telomeres are the hallmark of the transition from mononuclear H cells to multinuclear RS cells in EBVnegative Hodgkin cell lines and in classical EBV-negative HL. We recently showed that EBV-negative RS cells represent end-stage tumor cells, in which further nuclear division becomes impossible because of sustained telomere loss, shortening and aggregation. 1 However, nothing is known about the 3D telomere organization in LMP1-expressing H and RS cells of EBV-associated Hodgkin's disease (HD). In this study, we document 3D telomere dynamics in LMP1-expressing H and RS cells and show conformity with those observed in EBV-negative HD analyzed in parallel.