Interphase chromosomes form distinct spatial domains called chromosome territories (CTs). The position of CTs is known not to be at random and is related to chromosome size and gene density. To elucidate how CTs are arranged in primate proliferating fibroblasts and whether the radial position of CTs has been conserved during primate evolution, several specific CTs corresponding to conserved chromosomes since the Simiiformes (human 6, 12, 13, and 17 homologous CTs) have been studied in 3D preserved interphase nuclei from proliferant cells of two New World monkey species (Lagothrix lagothricha, Saimiri sciureus) and in human by three-dimensional fluorescent in situ hybridization (3D-FISH). Our results indicate that both gene-density and chromosome size influence chromosome territory arrangement in the nucleus. This influence is greater for chromosome-size than for gene-density in the three species studied. A comparison of the radial position of a given CT and its homolog in the species analyzed suggests similar CT distributions for homologous chromosomes. Our statistical analysis using the logit model shows that such homologous positionings cannot, however, be considered identical. © Springer-Verlag 2006.