Background Reports on fatty acids levels in multiple sclerosis remain inconclusive. Objective To determine the erythrocyte membrane fatty acid levels in multiple sclerosis patients and correlate with Kurtzke Expanded Disability Status Scale. Methods Fatty acid composition of 31 multiple sclerosis and 30 control individuals were measured by gas chromatography. Results The membrane phosphatidylcholine C20:4n – 6 concentration was lower in the multiple sclerosis patients when compared to that of the control group, P = 0.04 and it correlated inversely with the EDSS and FSS. Conclusion Decrease in C20:4n – 6 in the erythrocyte membrane could be an indication of depleted plasma stores, and a eflection of disease severity. Multiple Sclerosis 2009; 15: 759–762. http://msj.sagepub.com