A substantial amount of research has been conducted into the mental health of the UK military in recent years. This article summarises the results of the various studies and offers possible explanations for differences in findings between the UK and other allied nations. Post-traumatic stress disorder (PTSD) rates are perhaps surprisingly low amongst British forces, with prevalence rates of around 4% in personnel who have deployed, rising to 6% in combat troops, despite the high tempo of operations in recent years. The rates in personnel currently on operations are consistently lower than these. Explanations for the lower PTSD prevalence in British troops include variations in combat exposures, demographic differences, higher leader to enlisted soldier ratios, shorter operational tour lengths and differences in access to long-term health care between countries. Delayed-onset PTSD was recently found to be more common than previously supposed, accounting for nearly half of all PTSD cases; however, many of these had sub-syndromal PTSD predating the onset of the full disorder. Rates of common mental health disorders in UK troops are similar or higher to those of the general population, and overall operational deployments are not associated with an increase in mental health problems in UK regular forces. However, there does appear to be a correlation between both deployment and increased alcohol misuse and post-deployment violence in combat troops. Unlike for regular forces, there is an overall association between deployment and mental health problems in Reservists. There have been growing concerns regarding mild traumatic brain injury, though this appears to be low in British troops with an overall prevalence of 4.4% in comparison with 15% in the US military. The current strategies for detection and treatment of mental health problems in British forces are also described. The stance of the UK military is that psychological welfare of troops is primarily a chain of command responsibility, aided by medical advice when necessary, and to this end uses third location decompression, stress briefings, and Trauma Risk Management approaches. Outpatient treatment is provided by Field Mental Health Teams and military Departments of Community Mental Health, whilst inpatient care is given in specific NHS hospitals.