Background: Patients with Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) often present with a range of flu-like symptoms resembling sickness behavior as well as widespread pain and concentration deficits. The aim of this study was to explore the association between inflammatory markers previously shown to be related to fatigue severity in ME/CFS and common ME/CFS symptoms post-exertional fatigue, impaired cognitive processing, musculoskeletal pain and recurrent flu-like symptoms, and the moderating effect of sex on these associations. Methods: 53 adult patients diagnosed with ME/CFS at a specialist clinic were included in the study. Fasting blood plasma was analyzed using the Olink Proseek Multiplex Inflammation panel (beta-NGF, CCL11, CXCL1, CXCL10, IL-6, IL-7, IL-8, IL-10, IL-18, TGF-alpha, TGF-beta-1 and SCF) and BioRad Human Cytokine Type 1 assay (TNF-alpha). Participants rated the average severity of symptoms (0-10) based on the 2011 International Consensus Criteria of ME/CFS during a structured clinical interview. Associations between inflammatory markers and symptom severity were analyzed using bivariate correlations and moderated regression analyses bootstrapped with 5000 repetitions. Results and conclusions: Only beta-NGF was associated with the fatigue severity measure. However, higher levels of CCL11, CXCL10, IL-7, TNF-alpha and TGF-beta-1 were significantly associated with higher levels of impaired cognitive processing and musculoskeletal pain, and sex was a significant moderator for CXCL10, IL-7 and TGF-beta-1. Future studies should investigate the relationship between inflammatory markers and key symptoms in ME/CFS in a longitudinal design in order to explore if and for whom low-grade inflammation may contribute to illness development.