A total of 26 cases of "nonspecific" erosions and ulcers of the colonic mucosa are reported. The most common causes were previous abdominal irradiation or ischemic disease due to arteriosclerosis. The lesions were localized to all segments of the colon. Of the 26 cases, five (19.2%) had erosions (ie, not penetrating beyond the muscularis mucosae) and the remaining 21, ulcers (ie, penetrating beyond the muscularis mucosae). In seven of the 26 cases (26.9%) more than one ulcer was found in the same specimen. Erosions may heal completely by epithelial regeneration (ie, restitutio ad integrum) while ulcers usually heal by replacing scarring tissue. Thus, the two lesions may not be clinically synonymous. The relatively high proportion of erosions among nonspecific ulcerations of the colonic mucosa has not been previously pointed out in the literature.