Recent studies suggest that copy number variations (CNVs) encompassing several genes involved in neurodevelopmental pathways are associated with a variety of neuropsychiatric phenotypes, including developmental delay (DD), mental retardation (MR), and autism spectrum disorders (ASDs). Here we present eight patients in a cohort of ∼1,200 patients referred for clinical array CGH testing for various neurodevelopmental phenotypes, who were identified to carry small (<1.0 Mb with the majority <500 kb) either total gene or intragenic deletions encompassing critical synaptic and other neurodevelopmental genes. The presentations of these patients included variable degrees of DD, speech problems, learning disabilities, MR, autistic-like features, and mild non-specific dysmorphic features. These genes belong to four functional categories, including neuronal transcription factor genes (NFIA at 1p31.3, MEF2C at 5q14.3, and CAMAT1 at 1p36.23p36.31), neuron-specific splicing factor genes (RBFOX1 at 16p13.2p13.3), genes involved in synapse formation and maintenance (CNTNAP2 at 7q35 and LRFN5 at 14q21.2), and genes involved in neurotransmission (CHRNA7 at 15q13.3 and IL1RAPL1 at Xp21.2p21.3). Our report expands the list of neurodevelopmental genes deleted in various neurobehavioral phenotypes, expands the phenotypes caused by haploinsufficiency of previously reported critical neurodevelopmental genes, and elucidates the clinical relevance and need for careful clinical interpretation of some small CNVs <500 kb. This report also suggests that small clinically relevant deletions encompassing critical synaptic and other neurodevelopmental genes can present clinically with various neurobehavioral phenotypes, which implies the existence of overlapping neuronal pathways in the pathogenesis of these phenotypes. © 2011 Wiley-Liss, Inc.