Abstract Chiari 1.5 malformation, a variant of Chiari malformation, presents unique radiological features and clinical implications. This review aims to summarize the radiological characteristics of Chiari 1.5 malformation. Magnetic resonance imaging (MRI) is the gold standard for diagnosing Chiari 1.5 malformation. Key radiological findings include herniation of the cerebellar tonsils below the foramen magnum, accompanied by herniation of the brainstem and fourth ventricle. The extent of tonsillar herniation, as measured by the distance from the basion to the tip of the herniated tonsils, is a crucial parameter for diagnosis and surgical planning. In addition to tonsillar herniation, Chiari 1.5 malformation often presents with associated abnormalities such as syringomyelia, hydrocephalus, and craniocervical junction anomalies. Syringomyelia, characterized by the formation of fluid-filled cavities within the spinal cord, is a common finding and may contribute to neurological symptoms such as pain, weakness, and sensory deficits.