Purpose: Today patients with suspected diverticulitis are commonly imaged with a CT scan utilizing a variety of methods of contrast medium administration. Although CT with rectally administered colon contrast has demonstrated a high diagnostic accuracy, concerns have been raised over its safety in patients with diverticulitis. The following retrospective investigation was undertaken to answer this concern. Materials and methods: Between January, 1997, and July, 1999, 308 patients with suspected diverticulitis were examined in the Emergency Radiology Division of the Massachusetts General Hospital by means of a helical CT scan performed with rectally administered colon contrast material. The patients' CT findings were correlated with their clinical courses and/or surgical findings. Results: Of the 308 CT scans, 115 (37.3 %) were positive for diverticulitis. Of 193 patients without diverticulitis, 91 (47.1 % of patients without diverticulitis) had alternative diagnoses made by CT, such as small bowel obstruction, epiploic appendagitis, and urinary tract calculi. No complications due to colon contrast material were noted. Even in cases where there was free extraluminal air, no extravasated contrast material was seen. Rectally administered colon contrast was well tolerated by patients and provided excellent large bowel opacification. This method saved imaging time in an emergency setting, as there was no need to wait for oral contrast to reach the colon. Conclusion: Out of 308 CT scans, there were no complications from the use of rectally administered colon contrast material. No case of traumatic bowel perforation secondary to colon contrast material was observed. Rectally administered colon contrast material is safe in the CT examination of patients with suspected diverticulitis.