['Knowledge of the occurrence of malformations of cortical development (MCDs) and its relationship to hindbrain deformity in Chiari II malformation (CIIM) is limited.', 'To assess malformations of cortical development and its relationship to hindbrain deformity regarding Chiari II malformation.', 'Brain and cervical spinal MRI from 66 children (age range, 1-256\xa0days; mean age, 22.3\xa0days) with Chiari II malformation were retrospectively reviewed. If present, the type, number and location of malformations of cortical development were recorded. Hindbrain deformity was assessed for the level of the medullary kink, the descent of the pons and the shape of the fourth ventricle; these parameters were compared in children with and without malformations of cortical development.', 'Twenty children with malformations of cortical development were identified. Only periventricular nodular heterotopia was noted. The median level of the medullary kink was significantly lower in children with malformations of cortical development compared with children without it (P\u2009=\u20090.037). A low pontomesencephalic junction was identified more frequently in children with malformations of cortical development (65.0%), relative to children without malformations of cortical development (34.8%) (P\u2009=\u20090.045). The fourth ventricular shape was not significantly different in children with or without malformations of cortical development (P\u2009=\u20090.684).'] Is periventricular nodular heterotopia related to severity of the hindbrain deformity in Chiari II malformation?