Nicolaides-Baraitser Syndrome is a rare genetic condition that clinically presents with intellectual disabilities, facial and bone changes, and sparse hair. In Brazil, only one case has been previously reported without genetic confirmation. We present the case of an 8-year-old boy, clinically and genetically diagnosed with Nicolaides-Baraitser Syndrome, who developed autism spectrum disorder characteristics with a formal diagnosis at the age of eight. Diagnosing autism spectrum disorder in patients with intellectual disabilities is a clinical challenge requiring careful evaluation.