The ribosomal protein S6 kinase, 90 kb, polypeptide 3 gene (RPS6KA3) is responsible for Coffin-Lowry syndrome (CLS), which is characterized by intellectual disability (ID) and facial and bony abnormalities. This gene also affects nonsyndromic X-linked ID and nonsyndromic X-linked ID without bony abnormalities. Two families have been previously reported to have genetic microduplication including RPS6KA3. In the present study, we used array-comparative genomic hybridization (CGH) analysis with Agilent Human genome CGH 180K and detected a 584-kb microduplication spanning 19.92-20.50 Mb of Xp22.12 (including RPS6KA3) in the members of one family, including three brothers, two sisters, and their mother. The 15-year-old male proband and one of his brothers had mild ID and localization-related epilepsy, whereas his other brother presented borderline intelligence quotient (IQ) and attention-deficit-hyperactivity disorder (ADHD). One sister presented pervasive development disorder (PDD). Analysis of this family suggests that RPS6KA3 duplication is responsible for mild ID, ADHD, and localization-related epilepsy, and possibly for PDD.