Cologastric fistula has rarely been reported as a complication of percutaneous endoscopic gastrostomy (PEG). We encountered a patient in whom this problem went unrecognized for 2 years. After the initial PEG tube was changed, the second PEG tube was advanced into the colon, causing severe diarrhea. When a third PEG tube was inserted, acute peritonitis occurred because of colonic perforation. We discuss the mechanism of this complication and technical points related to its prevention.