Neural development is a highly orchestrated process that entails precise control of gene expression. Although microRNAs (miRNAs) have been implicated in fine-tuning gene networks, the roles of individual miRNAs in vertebrate neural development have not been studied in vivo. We investigated the function of the most abundant neuronal miRNA, miR-124, during spinal cord development. Neither inhibition nor overexpression of miR-124 significantly altered the acquisition of neuronal fate, suggesting that miR-124 is unlikely to act as a primary determinant of neuronal differentiation. Two endogenous targets of miR-124, laminin gamma 1 and integrin beta1, were identified, both of which are highly expressed by neural progenitors but repressed upon neuronal differentiation. Thus miR-124 appears to ensure that progenitor genes are post-transcriptionally inhibited in neurons.