Andersen-Tawil Syndrome (ATS) is a rare genetic disorder inherited in an autosomal dominant pattern caused by mutations in the KCNJ2 gene encoding Kir2.1 protein forming potassium ion channel, leading to disruption of cardiac and skeletal muscle repolarisation. Clinical symptoms include periodic paralysis, ventricular arrhythmia associated with QT prolongation and typical skeletal and facial dysmorphic features. The aim of the study was to present characteristic features of the rare Andersen-Tawil syndrome (ATS) within the face and oral cavity of a 9-year-old boy. The patient was diagnosed with Andersen-Tawil syndrome (OMIM#170390) at the age of 8 due to the positive family history, typical dysmorphic features, and the presence of mutation in the KCNJ2 gene confirmed by genetic testing. Typical manifestations of ATS were diagnosed: cardiac arrhythmia, short stature, scoliosis and clinodactyly. Clinical examination revealed typical facial dysmorphic features of ATS: broad forehead, triangular shape of the face, hypertelorism, microstomia, low-set ears, and mandibular retrognathism. Intraoral examination revealed: high-arched palate, crowding in the dental arches, hypomineralisation of enamel and high incidence of dental caries. Dental age assessment by Demirijan pointed to delayed development of permanent dentition. Cephalometric analysis revealed skeletal class II with high angle vertical jaws relation. Diagnosis of ATS requires high index of suspicion because of a great variability in the clinical manifestation of the syndrome. The subtle nature of the dysmorphic features often delays the diagnosis of this syndrome, and its potentially lethal cardiac arrhythmia remaining undetected.