Military psychiatry has recently generated a lot of interest. In contrast there is virtually no literature on military forensic psychiatry. The first section of the paper is a brief review of British military psychiatric services and recent data on the prevalence of mental illness in British armed forces personnel. The second section summarizes the relevant aspects of the British military judicial and penal systems including the practice of summary justice, the court martial system, and sentencing and corrective training. The third section of the paper addresses issues which are particular to forensic psychiatry, including mental defences in relation to the military, the military offences of malingering and impersonation, risk assessment in military contexts and the notion of ‘temperamental unsuitability’ to military service.