Truncating variants of the "MAGEL2" gene, one of the protein-coding genes within the Prader-Willi syndrome (PWS) critical region on chromosome 15q11, cause Schaaf-Yang syndrome (SYS)--a neurodevelopmental disorder that shares several clinical features with PWS. The current study sought to characterize the neurobehavioral phenotype of SYS in a sample of 9 patients with molecularly-confirmed SYS. Participants received an assessment of developmental/intellectual functioning, adaptive functioning, autism symptomatology, and behavioral/emotional functioning. Compared to individuals with PWS, patients with SYS manifested more severe cognitive deficits, no obsessions or compulsions, and increased rates of autism spectrum disorder.