Emergent imaging of the brain is often required to diagnose and manage serious and life-threatening conditions for children presenting to the emergency department. In an effort to reduce children's exposure to ionizing radiation, the use of magnetic resonance imaging (MRI) as an alternative to computed tomography (CT) is increasing. In some conditions, an urgent MRI rather than CT is critical for making management decisions. The purpose of this review is to highlight 3 emergency medical conditions—acute stroke, traumatic brain injury, and hydrocephalus—in which timely MRI of the brain is required for diagnosis and management. Another aim will be to guide providers in determining when and what limited MRI sequences of the brain can be used in lieu of CT in these emergency medical conditions.