Fragile X Syndrome (FXS) is a neurodevelopmental disorder caused by epigenetic silencing of FMR1 and loss of FMRP expression. Here we describe the establishment of an isogenic human pluripotent embryonic stem cell model of FXS. Using CRISPR/Cas9 to introduce indels in exon 3 of FMR1 and result in complete loss of FMRP (FMR1KO). We show that FMRP-deficient neurons exhibit a number of phenotypic abnormalities including neurite outgrowth and branching deficits and impaired electrophysiological network activity as measured by multi-electrode arrays. RNA-Seq and proteome analysis of FMRP-deficient neurons revealed transcriptional dysregulation in pathways related to neurodevelopment, neurotransmission, and the cell cycle.