The presentation of acute-onset hemiparesis in a teenager can be challenging and offers a wide differential diagnosis. We discuss the approach to the patient (which should begin with thorough history taking and physical examination) and advanced imaging as directed by the patient's signs and symptoms. We report the case of an otherwise well 17-year-old girl who presented to the pediatric emergency department with a 2-day history of left-sided weakness and difficulty ambulating. Her eventual diagnosis of Balo concentric sclerosis, a rare form of multiple sclerosis, is discussed.