Catatonia is a severe, multidimensional neurobehavioral, and motor syndrome that carries high rates of morbidity and mortality if untreated, or undertreated. Catatonia historically has been best characterized in adult individuals with psychiatric syndromes such as bipolar disorder, major depressive disorder, and schizophrenia. However, in recent years, there has been increased awareness of catatonia in other populations. The risk of catatonia is now better appreciated in persons with medical etiologies (e.g., anti-NMDA receptor encephalitis); children and adolescents; persons with neurodevelopmental disabilities (NDD) like autism spectrum disorder (ASD); and in those with neurogenetic syndromes such as Phelan McDermid syndrome (PMS) or Down syndrome (DS). Diagnosis and treatment of individuals with NDD who develop catatonia requires: The purpose of its chapter is to provide an overview and summary of the recent literature focused on catatonia in individuals with underlying NDD, and to have a discussion of the experience of an individual with Kleefstra syndrome (KS) who developed catatonia.