Research of military personnel who deployed to the conflicts in Iraq or Afghanistan has suggested that there are differences in mental health outcomes between UK and US military personnel.

To compare the prevalence of post-traumatic stress disorder (PTSD), hazardous alcohol consumption, aggressive behaviour and multiple physical symptoms in US and UK military personnel deployed to Iraq.

Data were from one US (n = 1560) and one UK (n = 313) study of post-deployment military health of army personnel who had deployed to Iraq during 2007–2008. Analyses were stratified by high- and low-combat exposure.

Significant differences in combat exposure and sociodemographics were observed between US and UK personnel; controlling for these variables accounted for the difference in prevalence of PTSD, but not in the total symptom level scores. Levels of hazardous alcohol consumption (low-combat exposure: odds ratio (OR) = 0.13, 95% CI 0.07–0.21; high-combat exposure: OR = 0.23, 95% CI 0.14–0.39) and aggression (low-combat exposure: OR = 0.36, 95% CI 0.19–0.68) were significantly lower in US compared with UK personnel. There was no difference in multiple physical symptoms.

Differences in self-reported combat exposures explain most of the differences in reported prevalence of PTSD. Adjusting for self-reported combat exposures and sociodemographics did not explain differences in hazardous alcohol consumption or aggression.