The chromosome formula of Phloeomys cumingi is described for the first time. The diploid number is 40 in both sexes, the fundamental number is 60. The 38 autosomes are divided into 5 pairs of submetacentrics, 4 pairs of metacentrics, 6 pairs of large acrocentrics and 4 pairs of small acrocentrics. The sex chromosomes are large and rich in C-positive heterochromatin. The comparative analysis of the chromosomes of Phloeomys with those of Mus musculus and Rattus norvegicus puts forward numerous analogies between these 3 species. According to the comparison of the chromosomes of Phloeomys with the ancestral karyotype of the Cricetidae, eleven chromosome pairs at least have conserved their original G-banding pattern. Although chromosome data reveal a close relationship between Phloeomys and Muridae, they do not exclude the possible belonging of this species to a separate family, that of Phloeomyidae.