Idiopathic REM sleep behavior disorder (iRBD) is one of the most significant prodromal manifestations of synucleinopathies. Different predictive biomarkers for iRBD conversion have been investigated, but scarce data are present in literature about the predictive role of cerebrospinal fluid (CSF) biomarkers. In this review, we focus on CSF biomarkers in patients with both iRBD and RBD associated with synucleinopathies to explore their potential predictive power.