In multiple sclerosis (MS), serum levels of ICAM-1 were elevated during acute exacerbations and were therefore proposed as a marker of disease activity, but the potential of this molecule as an indicator of long-term activity, i. e. the progression of the disease outside acute exacerbations, is not known. We therefore measured sICAM-1 levels by an enzyme-linked immunosorbent assay in 26 patients with active relapsing-remitting (RR) MS (at least two relapses in the preceding 2 years, but not within the last 30 days), in 10 patients with active secondary-progressive MS (progression of at least one point on the EDSS and/or two relapses in the preceding 2 years, but not within the last 30 days), in 8 patients with stable RR MS (no relapse and no progression during the last two years), and in 16 healthy controls. There was no significant difference between the different MS subtypes and healthy controls, nor within the different MS subtypes. Thus, while sICAM-1 may be useful to indicate short-term activity of MS in terms of relapses and MRI activity, this does not hold true for the long-term activity of MS outside acute exacerbations.