PURPOSE: To perform virtual colonoscopy using electron beam tomography(EBT) in potients in whom a colonicmass was present, and to compare the results with those obtained using barium enema, colonoscopy and grosspathologic specimens. MATERIALS AND METHODS: Ten patients in whom colonic masses were diagnosed by either bariumenema or colonoscopy were involved in this study. There were nine cases of adenocarcinoma and one of tubulovillousadenoma. Using EBT preoperative abdominopelvic CT scans were performed. Axial scans were then three-dimensionallyreconstructed to produce virtual colonoscopic images and were compared with barium enema, colonoscopy and grosspathologic specimens. Virtual colonoscopic images of the masses were classified as either 1)polypoid, 2)sessile,3)fungating, or 4)annular constrictive. We also determined whether ulcers were present within the lesions andwhether there was obstruction. RESULT: After virtval colonoscopy, two lesions were classified as polypoid, oneas sessile, five as fungating and two as annular constrictive. Virtual colonoscopic images showed good correlationwith the findings of barium enema, colonoscopy and gross pathologic specimens. Three of six ulcerative lesionswere observed on colonoscopy; in seven adenocarcinomas with partial or total luminal obstruction, virtualcolonoscopy visualized the colon beyond the obstructed sites. In one case, barium contrast failed to pass throughthe obstructed portion and in six cases, the colonoscope similarly failed. CONCLUSION: Virtual colonoscopiescorrelated well with barium enema, colonoscopy and gross patholoic specimens. They provide three dimensionalimages of colonic masses and are helpful for the evaluation of obstructive lesions.