MicroRNAs are a recently discovered class of small non-coding RNAs that play a key role in post-transcriptional gene regulation during development and disease. MicroRNAs are abundant in the nervous system and have already been shown to have an important function during neuronal patterning and cell specification. It is now becoming increasingly evident that they are also essential for synaptic development and that they might contribute to the etiology of neuronal diseases characterized by synaptic dysfunction. This review focuses on the recent examples that describe a function of microRNAs in synapse formation and plasticity, and discusses how the microRNA pathway might be exploited to treat neurologic diseases.