Objectives – Epidemiological studies strongly indicate an infectious involvement in multiple sclerosis (MS). Epstein–Barr virus (EBV), to which all multiple sclerosis patients are seropositive, is also interesting from an epidemiological point of view. We have reported a cluster of MS patients with 8 members from a small Danish community called Fjelsø. To further evaluate the role of EBV in MS we have investigated the distribution of EBV subtypes in cluster members and in control cohorts. Materials and methods – Blood mononuclear cells were isolated from cluster members, unrelated MS patients, healthy controls, including healthy schoolmates to the Fjelstø cluster patients and finally from persons with autoimmune diseases in order to investigate the number of 39 bp repeats in the EBNA 6-coding region in the EBV seropositive individuals. Results – We observed a preponderance of the subtype with 3 39 bp repeats in the EBNA 6-coding region both in the MS patients and the healthy controls. In the Fjelsø cluster all 8 cluster members were harbouring this subtype, which is significantly different from the finding in healthy controls (n = 16), which include 8 schoolmates to the cluster members and 8 randomly selected healthy persons (Fischer's exact test P=0.0047), and also compared to all non-clustered individuals studied (P=0.017). Conclusion – Infection with the same subtype of EBV links together the 8 persons from the Fjelso cluster who later developed MS. This finding adds to the possibility that development of MS is linked to infection with EBV.