This study was undertaken to assess the damage caused by Pomphorhynchus bulbocolli to Catostomus commersoni (white sucker). Three specimens of C. commersoni were collected during early September 2014 via gill net from Canadarago Lake (Otsego County, New York), then dissected and examined for intestinal parasites. One C. commersoni, collected from a tributary of Otsego Lake (Otsego County, New York), was used as a control in this study because it was not infected with intestinal helminths. Upon dissection, damage to the fish intestine was macroscopically visible, with the intestine perforated when infected with P. bulbocolli. Intestines observed to be infected with P. bulbocolli were opened with a longitudinal incision and fixed in neutral buffered formalin with the acanthocephalans remaining attached. Histological sections of intestine with P. bulbocolli attached were compared with histological sections of intestine in which no worms were present. Examination of sections revealed full penetration of the intestinal wall and tissue destruction to the mucosa, submucosa, stratum compactum, and circular and longitudinal muscle layers, as well as an extensive host immune response in the form of proliferation of cells at the sites of wounds. While these results were consistent with previous histopathological studies on this host and parasite species, the occurrence of pockets of hyaline degeneration in the muscularis reported here is a new finding for this host–parasite system, and it appears to be quite rare in the parasitological literature. It is hypothesized that the presence of hyaline degeneration may be related to secretion of trypsinlike proteins from the presoma of the acanthocephalan, a phenomenon suggested previously for the congener Pomphorhynchus laevis. The host–parasite interaction involving physical damage, secretion of enzymes, and an extensive host immune response may be the cause of the damage, but further research is needed to investigate the nature of these interactions.