Traumatic brain injuries (TBIs) affect more than 1.4 million Americans annually. Trauma nurses caring for these patients routinely perform serial neurologic assessments, including pupillary examinations. While trauma nurses are likely familiar with basic components of the pupillary examination, some confusion about more specific aspects of the examination and the physiologic basis of the pupillary response may still remain, particularly as it pertains to patients with TBI. Therefore, the purpose of this article is to identify the key components of a pupillary examination and its associated physiologic response. A case study is provided to illustrate the application of this information among patients with TBI.