The Joint Commission issues Sentinel Event Alerts periodically to highlight emerging patient safety issues and stimulate innovative approaches to addressing these threats. The overuse of diagnostic imaging, particularly computed tomographic (CT) scans, poses patient safety risks due to excess radiation exposure. More than 70 million CT scans are performed in the United States every year, and the radiation exposure from these scans may lead to thousands of cancer-related deaths. This alert reviews specific strategies organizations should take to minimize radiation risks, including educating physicians on appropriate test utilization, standardizing equipment and radiation dosage, and promoting a culture of safety. An AHRQ WebM&M commentary discusses factors that may contribute to overutilization of diagnostic imaging, with consequent short- and long-term risks to patients.