MicroRNAs (miRNAs) are secreted from cells as either protein bound or enclosed in extracellular vesicles. Circulating liver-derived miRNAs are modifiable by weight-loss or insulin-sensitizing treatments, indicating that they could be important biomarkers candidates for diagnosis, monitoring, and prognosis in NAFLD (non-alcoholic liver disease) and NASH (non-alcoholic steatohepatitis). Unfortunately, the non-invasive diagnosis of NASH and fibrosis remains a key challenge, which limits case finding. Current diagnostic guidelines therefore recommend liver biopsies, with risks of pain and bleeding for the patient and substantial healthcare costs. Here, we summarize mechanisms of RNA secretion, and review circulating RNAs associated with NAFLD and NASH for their biomarker potential. Few circulating miRNAs are consistently associated with NAFLD/NASH: miR-122, miR-21, miR-34a, miR-192, miR-193 and the miR-17-92 miRNA-cluster. The hepatocyte-enriched miRNA-122 is consistently increased in NAFLD and NASH but decrease in liver cirrhosis. Circulating miR-34a, part of an existing diagnostic algorithm for NAFLD, and miR-21 are consistently increased in NAFLD and NASH. MiR-192 appears to be prominently upregulated in NASH compared with NAFDL, whereas miR-193 was reported able to distinguish NASH from fibrosis. Various members of miRNA cluster miR-17-92 are reported associated with NAFLD and NASH, although with less consistency. Several other circulating miRNAs have been reported associated with fatty liver in few studies, indicating the existence of more circulating miRNAs with relevant as diagnostic markers for NAFLD or NASH. Thus, circulating miRNAs show potential as biomarkers of fatty liver disease, but more information about phenotype specificity and longitudinal regulation is needed.