IntroductionMotor stereotypies represent a typical example of the difficulty in distinguishing non-clinical behaviors (physiological and transient) from symptoms or among different disorders [“primary stereotypies,” associated with autistic spectrum disorder (ASD), intellectual disabilities, genetic syndromes, and sensory impairment]. The aim of this study was to obtain an accurate assessment on the relationship between stereotypies and neurodevelopmental disorders.MethodsWe studied 23 children (3 girls), aged 36–95 months, who requested a consultation due to the persistence or increased severity of motor stereotypies. None of the patients had a previous diagnosis of ASD. The assessment included the Motor Severity Stereotypy Scale (MSSS), the Repetitive Behavior Scale-Revised (RBS-R), the Raven’s Colored Progressive Matrices, the Child Behavior CheckList for ages 1½–5 or 4–18 (CBCL), the Social Responsiveness Scale (SRS), and the Autism Diagnostic Observation Schedule-second edition (ADOS 2).ResultsAll patients were showing motor stereotypies for periods of time varying from 6 to 77 months. The MSSS showed that each child had a limited number of stereotypies; their frequency and intensity were mild. The interference of stereotypies was variable; the impairment in daily life was mild. The RBS-R scores were positive for the subscale of “stereotypic behaviors” in all children. Moreover, several children presented other repetitive behaviors, mainly “ritualistic behavior” and “sameness behavior.” All patients showed a normal cognitive level. The CBCL evidenced behavioral problems in 22% of the children: internalizing problems, attention, and withdrawn were the main complaints. On the SRS, all but one of the tested patients obtained clinical scores in the clinical range for at least one area. On the ADOS 2, 4 patients obtained scores indicating a moderate level of ASD symptoms, 4 had a mild level, and 15 showed no or minimal signs of ASD.DiscussionMotor stereotypies in children with normal cognitive level represent a challenging diagnostic issue for which a finely tailored assessment is mandatory in order to define a precise developmental profile. Thus, careful and cautious use of standardized tests is warranted to avoid misdiagnosis. Furthermore, it is hard to consider motor stereotypies, even the primary ones, exclusively as a movement disorder.