Colonic perforation during flexible colonoscopy is a rare but recognized complication. We reviewed 4,593 colonoscopies performed from 1984 to 1989. The perforation rate for diagnostic colonoscopy was 0.17% (6/3,538) and for therapeutic colonoscopy it was 2% (21/1,055). Four perforations of the right colon occurred at a site proximal to the level of the impacted colonoscope. The lesions being evaluated were obstructive in nature: two diverticular strictures (sigmoid colon), one ischemic stricture (descending colon), and one annular carcinoma (descending colon). The four perforations occurred in the right colon and manifested as distension with pneumoperitoneum or retroperitoneal emphysema. Operative management included total abdominal colectomy in two patients (ileoproctostomy in one and ileostomy in one) and right colectomy in two. Outcome was favorable in all cases.