Objective: The purpose of this study was to investigate the levels of non-esterifi ed fatty acids in plasma from patients with multiple sclerosis and further to correlate these fi ndings with the neurological profi le as measured by the Kurtzke Expanded Disability Status Scale. Methods: Plasma non-esterifi ed fatty acids and esterifi ed fatty acids from 30 control subjects and 31 patients with multiple sclerosis were measured by gas chromatography. Results: Non-esterifi ed fatty acids C18:2n-6, C20:4n-6, C16:1n-7, C18:1n-7, C18:1n-9, C14:0, C16:0 and C18:0 were signifi cantly increased in plasma from patients with multiple sclerosis, P ≤ 0.01, while esterifi ed fatty acid C18:2n-6 was decreased, P = 0.003. Fatty acid PC C16:1n-7 and non-esterifi ed fatty acids C16:1n-7, C18:1n-7 and C18:1n-9 showed positive and fatty acids C18:1n-9, C20:0, C22:0 and C24:0 showed inverse correlations with the Functional System Scores. Conclusions: We have identifi ed increased monounsaturated non-esterifi ed fatty acids in plasma from patients with multiple sclerosis as indicative of a worse disease outcome. Further, the decrease in fatty acid C18:2n-6, with increases in non-esterifi ed fatty acids C18:2n-6 and C20:4n-6, suggested a role for