The human appendix vermiformis is regarded as an evolutionarily vestigial organ, although it has presumptive immune system functions and appears to support beneficial bacterial gut flora, both of which could influence cancer progression. A review of the comparative anatomy of the mammalian appendix reveals a significantly longer appendix in herbivores than in carnivorous animals. The lengthier appendix vermiformis in herbivores has been associated with the presence of cellulose-digesting bacteria that colonize the structure. In light of recent studies that have reported the digestion of small amounts of cellulose in humans and the preventive effects of a vegetarian diet on colon cancer, we conducted a retrospective study of abdominal CT scans of 60 colon cancer patients and 60 healthy people to investigate a possible relationship between colon cancer and appendix vermiformis length. The mean length of the appendix in cancer patients [65.178 mm +/- 13.46 (SD)] was shorter than that in the healthy control group [101.99 mm +/- 16.58 (SD)] and the difference was statistically significant (P < 0.001). Statistical analysis demonstrated that the ages of the cancer patient group and the control group did not differ significantly (P = 0.534). The results of the present study indicate that the appendix is not merely a vestigial structure or regressed lymphoid tissue, but rather an organ that could be critical in the development of colon cancer, whether as a result of congenital or acquired appendicular factors. Clin. Anat. 27:498-502, 2014. (c) 2014 Wiley Periodicals, Inc.