Psychiatric syndromes, including schizophrenia, mood and autism spectrum disorders are characterised by a complex range of symptoms, including psychosis, depression, mania, and cognitive deficits. While the mechanisms driving their pathophysiology is complex and remains largely unknown, advances in the understanding of gene association and gene networks are providing significant clues to the aetiology. In recent years small non-coding RNA known as microRNA (miRNA) have emerged as potential players in the pathophysiology of mental illness. These small RNAs regulate mRNA stability and translation on a broad scale through their capacity to target hundreds of mRNA transcripts and influence entire gene networks. There is evidence to suggest that numerous miRNA are dysregulated in postmortem neuropathology of neuropsychiatric disorders and strong genetic support for association of both miRNA genes and their targets with these conditions. There are also a number of studies that implicate miRNA function in the action of antipsychotics and mood stabilisers, suggesting that these small RNAs may play a role in existing therapy or represent influential targets for future treatments. In this review, we discuss the accumulated evidence linking miRNA dysregulation and dysfunction with schizophrenia, bipolar disorder, major depressive disorder, and autism spectrum disorders, as well as their potential as biomarkers or therapeutics for these disorders. We further assess the functional roles of some of the outstanding miRNAs associated with these conditions, and how they may be influencing the development of psychiatric symptoms.