MicroRNAs are small non-coding RNAs that modulate gene expression post-transcriptionally. Discovered more than 15 years ago, their functions start to be unraveled. Increasing evidence points to an important functional role of microRNAs in brain development. In particular, miRNAs have recently been established to play a vital role in the mechanisms underlying the infantile rise in gonadotropin-releasing hormone (GnRH) production by neurons in the hypothalamus, a phenomenon necessary for the onset of puberty in mammals.