Objective: Chromosome 17q12 microdeletion is a rare genetic disorder resulting in multi-system disruption, including the central nervous system. This microdeletion results in a wide range of clinical manifestations, including developmental delay, cognitive deficits, behavioral impairments, and health problems. The purpose of this case study is to describe and inform researchers and practitioners regarding the neurobehavioral and neurocognitive presentation of a rare genetic disorder that is scientifically underserved due to the recent availability of testing. Improved understanding of the phenotypic variance and anticipated neurobehavioral deficits may promote early detection, monitoring, and intervention. Method: Based on review of records, genetic testing revealed a chromosome 17q12 microdeletion. Brain MRI revealed delayed myelination around the occipital horns and trigone of the lateral ventricles. Descriptive analysis of neuropsychological assessment data was done within a single-subject design of an 8-year-old male with history of language and motor delays, learning deficits, and increasingly impulsive behavior and provocative language. Results: Test results indicated global cognitive deficits, including significant (age-adjusted) declines in language and inhibition scores since 2008 and 2012 testing. Deficits were found across multiple areas of neurodevelopment, including executive functioning, visual and verbal memory and learning, visual construction, and fine motor speed. Memory for faces was average and a relative strength. Conclusion(s): This case study examines an 8 year-old male with 17q12 microdeletion. He presents as a more severe variant of developmental difficulties with marked executive dysfunction, relative to existing reports in the literature. These findings add to the phenotypic variability, neurodevelopmental course, and profile of such youngsters.