Definition of dysregulated immune components in multiple sclerosis may help in the identification of new therapeutic targets. Deviation of the interleukin 18 receptor 1 (IL18R1) is of particular interest since the receptor is critical for experimental neuroinflammation. The objective of this study was to determine whether expression of IL18R1 varies between multiple sclerosis patients and controls, and to test genetic association of IL18R1 with multiple sclerosis. We used quantitative real-time PCR to assess mRNA levels of IL18R1 in cerebrospinal fluid and peripheral blood mononuclear cells of 191 patients with multiple sclerosis, 61 patients with clinically isolated syndrome and 168 controls having other neurological disorders. Association was tested in 2153 patients with multiple sclerosis and 1733 controls using 13 tagging single nucleotide polymorphisms within the IL18R1 gene. We found that patients with multiple sclerosis had increased IL18R1 mRNA expression in both cerebrospinal fluid cells (p