The aetiology of adolescent idiopathic scoliosis (AIS) has been linked to many factors, such as asymmetric growth, neuromuscular condition, bone strength and genetic background. Recently, epigenetic factors have been proposed as contributors of AIS physiopathology, but information about the molecular mechanisms and pathways involved is scarce. Regarding epigenetic factors, microRNAs (miRNAs) are molecules that contribute to gene expression modulation by regulating important cellular pathways. We herein used Next-Generation Sequencing to discover a series of circulating miRNAs detected in the blood samples of AIS patients, which yielded a unique miRNA biomarker signature that diagnoses AIS with high sensitivity and specificity. We propose that these miRNAs participate in the epigenetic control of signalling pathways by regulating osteoblast and osteoclast differentiation, thus modulating the genetic background of AIS patients. Our study yielded two relevant results: 1) evidence for the deregulated miRNAs that participate in osteoblast/osteoclast differentiation mechanisms in AIS; 2) this miRNA-signature can be potentially used as a clinical tool for molecular AIS diagnosis. Using miRNAs as biomarkers for AIS diagnostics is especially relevant since miRNAs can serve for early diagnoses and for evaluating the positive effects of applied therapies to therefore reduce the need of high-risk surgical interventions.