We report on a patient with a recognizable phenotype of intellectual disability, multiple congenital anomalies, musculoskeletal anomalies and craniofacial dysmorphisms, carrying a de novo 0.4 Mb duplication of chromosome region 16p13.3 detected by SNP-array analysis. In addition, myopia, microcephaly and growth retardation were observed. The causal 16p13.3 duplication is one of the smallest reported so far, and includes the CREB binding protein gene (CREBBP, MIM 600140), whose haploinsufficiency is responsible for the Rubinstein-Taybi syndrome, and the adenylate cyclase 9 gene (ADCY9, MIM 603302). By comparing the clinical manifestations of our patient with those of patients carrying similar rearrangements, we confirmed that 16p13.3 microduplications of the Rubinstein-Taybi region result in a recognizable clinical condition that likely represents a single gene disorder. In addition, our case allowed us to define with more precision the smallest region of overlap (SRO) in all patients reported so far, encompassing only the CREBBP gene, and is useful to confirm and further define the phenotypic characteristics due to duplication of the CREBBP gene, being the first case of interstitial duplication with microcephaly and growth defects reported to date.