Background Although previous research provides insight into the role of neuroinflammation in idiopathic REM sleep behavior disorder, the association of this disorder with peripheral blood inflammatory markers remains unclear. Objective To investigate inflammatory cytokines in plasma samples in patients with idiopathic rapid eye movement sleep behavior disorder and to explore whether these markers are associated with prodromal symptoms of α‐synucleinopathies. Methods We collected plasma from patients with polysomnographically confirmed idiopathic rapid eye movement sleep behavior disorder without parkinsonism or dementia (n = 54) and from healthy controls (n = 56). The following cytokines were measured: interleukin‐1β, interleukin‐2, interleukin‐6, interleukin‐10, and tumor necrosis factor‐α. The idiopathic REM sleep behavior disorder patients underwent sleep, motor, cognitive, olfactory, and autonomic testing. Results The anti‐inflammatory cytokine, interleukin‐10, levels in the idiopathic rapid eye movement sleep behavior disorder group were significantly upregulated compared to the control group (P = 0.022), but this difference did not withstand Bonferroni correction. The other proinflammatory cytokine levels did not differ between the groups. No correlation was found between the cytokine levels and any clinical variable. Conclusions Our data do not provide evidence supporting the role of peripheral inflammation in idiopathic rapid eye movement sleep behavior disorder. However, considering the limited statistical power because of the small sample size, further large‐scale longitudinal studies with a broader spectrum of cytokines are needed to clarify this issue. © 2019 International Parkinson and Movement Disorder Society