Patients with Chiari malformation Type I (CM-I) most commonly present with chronic symptoms. A search of the current medical literature revealed scant information regarding acute presentations of CM-I in either pediatric or adult patients. The authors report on two children who presented with rapidly worsening neurological symptoms attributable to a previously undiagnosed CM-I. One patient became profoundly hypopneic with dysphagia and right hemiparesis over a less than 48-hour period. The second patient presented with a few days of worsening right hemiparesis, gait disturbance, and anisocoria. In addition to a CM-I, magnetic resonance imaging in the second patient revealed a holocord syrinx. Following urgent posterior fossa decompression, both patients rapidly improved in the 24 hours immediately following surgery and continued to improve in the subsequent weeks. Few reports detail acute symptoms due to CM-I and those that do exist almost exclusively involve adult patients. Although seemingly rare, the clinician should consider CM-I in the differential diagnosis in pediatric patients presenting with acute brainstem or long tract signs.