Introduction Most patients with multiple sclerosis (MS) will experience at least one relapse. Relapses may be mild, moderate, or severe. Disease modifying therapies (DMTs) modestly reduce the number of relapses at a mean annual cost of £12500. There are little data on the cost of MS relapses.

Aim We sought to identify the costs associated with mild, moderate and severe relapses and compare these figures with the costs of DMTs.

Methods Patients with an MS relapse from March 2011 until January 2012 completed a questionnaire detailing time lost from work, approximate loss of earnings and other expenses. We calculated the overall costs of mild (requiring no treatment or oral prednisolone), moderate (requiring outpatient intravenous methylprednisolone) and severe (requiring hospitalisation) relapses. The cost of a severe relapse was calculated using an itemised list of all services utilised during hospital admissions in 2010.

Results There were a total of 38 relapse episodes in 33 patients (20 women), 4 mild, 27 moderate, and 7 severe relapses. Fourteen patients were not receiving DMTs. The median cost of a mild relapse was £127 with a mean of 5 days lost from work (median cost=£553, n=2). For moderate relapses a median cost of £503 (range £148–£3319) was incurred with mean sick leave of 6.5 days (median cost=450, n=16). For a severe relapse mean length of stay was 10 days with a median hospitalisation cost of £3856.

Conclusion The costs of a relapse are proportional to its severity. The cost of DMTs may be partially offset by the reduction in relapses.