Cytogenetic analysis of an adenocarcinoma of the large bowel with some villous features revealed consistent chromosome changes: trisomy of chromosomes No. 7, 12, and 20 and a deletion of part of the long arm of a chromosome No. 12. Examination of the chromosome findings in previously published cases of large bowel cancers and the data presented in this paper lead us to suggest that trisomy No. 7 and 12q- may be nonrandom (primary) karyotypic changes in a subgroup of large bowel cancers.