Using a previously identified human CENPC cDNA fragment, we have isolated cDNA clones corresponding to the complete mouse Cenpc coding sequence. Using these cDNAs as probes to genomic libraries, we have isolated genomic clones corresponding to the mouse and human genes and also to a mouse pseudogene. In situ hybridization mapping of these genes reveals that the human gene maps to 4q12-q13.3 and the mouse gene to 5E2-E5. These sites are in a region of linkage group conservation between the two species. Secondary sites are present in man on chromosome 12q21.2-q21.33 and in mouse on chromosome 2B. This mouse secondary site is a pseudogene on the basis of DNA sequence. These secondary sites are not syntenic in the two species.