Arnold-Chiari syndrome is characterized by enlargement of the cerebellar tonsils going through the foramen magnum, reaching the spinal canal. The syndrome has 4 ratings: type I (asymptomatic in childhood), types II and III (diagnosed in the second week life), and type IV (incompatible with life). Oral alterations are rarely described, tooth agenesis being the most common. This study aims to report the case of a 3-year-old patient who is an Arnold-Chiari syndrome type II carrier with dental alterations. The case was evaluated by the hospital dentistry team because of the dental changes. Based on clinical finds, a skull x-ray (posterior-anterior projection, oblique lateral x-ray) where dental anomaly of number (supranumerary teeth) and enamel hypoplasia was observed. Topic fluor applications and monitoring are being made. The consistent clinical presentation provides further evidence of the dental characteristics of Arnold-Chiari type II syndrome patients. Arnold-Chiari syndrome is characterized by enlargement of the cerebellar tonsils going through the foramen magnum, reaching the spinal canal. The syndrome has 4 ratings: type I (asymptomatic in childhood), types II and III (diagnosed in the second week life), and type IV (incompatible with life). Oral alterations are rarely described, tooth agenesis being the most common. This study aims to report the case of a 3-year-old patient who is an Arnold-Chiari syndrome type II carrier with dental alterations. The case was evaluated by the hospital dentistry team because of the dental changes. Based on clinical finds, a skull x-ray (posterior-anterior projection, oblique lateral x-ray) where dental anomaly of number (supranumerary teeth) and enamel hypoplasia was observed. Topic fluor applications and monitoring are being made. The consistent clinical presentation provides further evidence of the dental characteristics of Arnold-Chiari type II syndrome patients.