BACKGROUND: Chiari malformation type 2 (CMII) is a herniation of anatomical structures of the posterior fossa due to myelomeningocele (MMC), the most common neural tube defect. Most patients with MMC exhibit radiologic signs of CMII. The study aimed to evaluate radiological parameters of the posterior fossa in patients undergoing surgery for CMII, with the goal of establishing structural indications for surgical treatment to prevent clinical manifestations and life-threatening symptoms. METHODS: The study included all constitutive patients with CMII diagnosed between 2016 and 2018. The following measurements were taken and analyzed for associations: size of the fourth ventricle, the McRae line, the depth of tonsillar herniation, the amount of cerebrospinal fluid (CSF) at the C0 level, the presence of syringomyelia, hydrocephalus, ventriculoperitoneal shunt (VPS) implantation, and supracerebellar cistern. RESULTS: The length of the McRae line and the depth of tonsillar herniation were strongly positively correlated. There was a negative relationship between the length of McRae line and the amount of CSF at the C0 level. There was a strong positive correlation between depth of tonsillar herniation and hydrocephalus. MMC and VPS implantation were associated with a larger depth of tonsillar herniation. CONCLUSIONS: The depth of the tonsillar herniation may not be the most viable finding influencing operative indication due to its dependency on the length of the McRae line. A small amount of CSF at the level of foramen magnum also should not necessarily be considered an early sign of syringomyelia. Ventriculoperitoneal shunt implantation seems not to influence the depth of tonsillar herniation.