Purpose: Medical imaging is an increasingly important source of radiation exposure for the general population, and there are risks associated with such exposure; however, recent studies have demonstrated poor understanding of medical radiation among various groups of health care providers. This study had two aims: (1) analyze physicians' knowledge of radiation exposure and risk in diagnostic imaging across multiple specialties and levels of training, and (2) assess the effectiveness of a brief educational presentation on improving physicians' knowledge. Methods: From 2014 to 2016, 232 health care providers from multiple departments participated in an educational presentation and pre- and postpresentation tests evaluating knowledge of radiation exposure and risk at a large academic institution. Results: Knowledge of radiation exposure and risk was relatively low on the prepresentation test, including particularly poor understanding of different imaging modalities, with 26% of participants unable to correctly identify which modalities expose patients to ionizing radiation. Test scores significantly increased after the educational presentation. Radiologists had higher prepresentation test scores than other specialties, and therefore less opportunity for improvement, but also demonstrated improvement in radiation safety knowledge after education. Aside from radiology, there was no significant difference in initial knowledge of radiation exposure and risk among the other specialties. Conclusions: Providers' knowledge of radiation exposure and risk was low at baseline but significantly increased after a brief educational presentation. Efforts to educate ordering providers about radiation exposure and risk are needed to ensure that providers are appropriately weighing the risks and benefits of medical imaging and to ensure high-quality, patient-centered care.