The aim of this study was to characterise severe open tibial shaft fractures sustained by UK military personnel over 10-years of combat and to determine the infection rate and factors that influence it. The UK military Joint Theatre Trauma Registry was searched and X-rays, clinical notes and microbiological records were reviewed for all patients. One hundred GA III open tibia fractures in 89 patients were identified. Three fractures were not followed up for 12-months and were therefore excluded. Twenty-two (23%) of the remaining 97 tibial fractures were complicated by infection requiring surgical treatment, with S. aureus being the causative agent in 13/22 infected fractures (59%). Neither injury severity, mechanism, the use of an external fixator, the need for vascularised tissue transfer or smoking status were significantly associated with infection. Bone loss was significantly associated with subsequent infection (p<0.0001). Most infection in combat open tibia fractures is caused by familiar organisms i.e. S. aureus. The use of external fixators to temporarily stabilise fractures is not associated with an increased risk of subsequent infection. While the overall severity of a casualty's injuries was not associated with infection, the degree of bone loss from the fracture was.