BACKGROUND: We investigated whether military personnel involved in chemical warfare agent research at Porton Down had increased rates of mortality or cancer incidence.

METHODS: This was a historical cohort study comprising male UK veterans who participated in the 'Service Volunteer Programme', 1941-89, identified from Porton Down experiment books, and a comparison group of similar 'non-Porton Down' veterans identified from military personnel files. Of 19 233 records retrieved for each group, 18 133 (94%) Porton Down and 17 591 (92%) non-Porton Down were included in our analytical sample. Mortality and cancer incidence data were obtained from national registries up to December 2019.

RESULTS: Over a median follow-up of 48.1 years, 10 935 Porton Down veterans (60.3%) and 10 658 non-Porton Down veterans (60.6%) had died. After adjustment for age, year of birth and military service characteristics, overall, Porton Down veterans had a 6% higher rate of all-cause mortality compared with non-Porton Down veterans [hazard ratio (HR) = 1.06, 95% confidence interval (CI) 1.03-1.09]. For cause-specific mortality, Porton Down veterans had higher rates of death from genitourinary diseases (HR = 1.34, 95% CI 1.05-1.70) and deaths attributable to alcohol (HR = 1.44, 95% CI 1.07-1.94), with weaker associations observed for deaths from infectious and parasitic diseases (HR = 1.32, 95% CI 0.99-1.78), lung cancer (HR = 1.10, 95% CI 1.01-1.20) and external causes (HR = 1.15, 95% CI 1.00-1.32). Associations with all-cause mortality were stronger for veterans who attended Porton Down between 1960 and 1964 (HR = 1.34, 95% CI 1.19-1.50); likelihood-ratio test, P = 0.006. There was no association between attendance at Porton Down and overall cancer incidence (HR = 1.00, 95% CI 0.95-1.03).

CONCLUSIONS: Overall, mortality rates were slightly higher in Porton Down veterans, but there was no difference in cancer incidence. Associations for mortality were stronger in Porton Down veterans who attended in the early 1960s.