Phelan-McDermid syndrome is caused by the loss of terminal regions of different sizes at 22q13. There is a wide range of severity of symptoms in patients with a 22q13 deletion, but these patients usually show neonatal hypotonia, global developmental delay, and dysmorphic traits. We carried out a clinical and molecular characterization of a patient with neonatal hypotonia and dysmorphic features. Array-based comparative genomic hybridization showed an 8.24 Mb terminal deletion associated with a 0.20 Mb duplication. Characterization of patients with Phelan-McDermid syndrome both clinically and at the molecular level allows genotype-phenotype correlations that provide clues to help elucidate the clinical implications.