Grisel's syndrome (GS) is a rare neurosurgical condition involving nontraumatic rotatory subluxation of the atlantoaxial joint. This case report presents a two-month-old infant girl, the youngest reported case of this syndrome based on our literature review to the date of this publication. The infant was initially referred to our hospital as a case of the arachnoid cyst but was subsequently neuroradiologically diagnosed with GS, which was believed to be secondary to a retropharyngeal abscess. After developing weakness and developmental delay as well as failing conservative management for two years, the infant underwent C1 laminectomy and occipitocervical sublaminar wire fusion with favorable outcomes. GS should be considered a differential even if the patient does not present with typical signs such as torticollis and neck pain. If not identified early and treated effectively, it can result in severe neurological damage. The management plan largely depends on the Fielding-Hawkins grade of subluxation and the timing of diagnosis.