Background Multiple sclerosis (MS) is the most common serious neurological disorder in young people in the UK. In the course of an analysis of trends in occupational mortality in England and Wales over the past thirty years, we observed a striking excess of deaths from MS among men in the Armed Forces, which prompted more detailed investigation.

Methods We analysed data on underlying cause of death and last full-time occupation for 3,688,916 deaths among men aged 20–74 years in England and Wales during 1979–2010, calculating proportional mortality ratios (PMRs) standardised for age. We compared PMRs from MS and from motor neurone disease (MND) in the armed forces and in various other occupational groups selected for comparison.

Results The overall PMR for MS in the armed forces during 1979–2010 was 242 (95% CI: 202–288). The excess was apparent in each of three separate decades of study (PMRs, ranging from 220 to 255), and across the entire age range. There was no parallel increase in PMRs for MND, and PMRs for MS were not consistently elevated to the same degree in comparator occupations.

Conclusions The observed pattern of mortality is unlikely to have arisen by chance or from denominator bias. It may be that some men who leave the Armed Forces because of MS fail to get civilian jobs, and are therefore recorded on their death certificates as last working in the military. Other possible explanations will be discussed.