Background. Combat is associated with high-energy explosive injuries, often resulting in open tibial fractures complicated by nonunion and infection. We characterize the infections seen in conjunction with combat-associated type III tibial fractures. Methods. We performed a retrospective medical records review to identify US military service members wounded in Iraq or Afghanistan with open diaphyseal tibial fractures who were admitted to our facility (Brooke Army Medical Center, Fort Sam Houston, Texas) between March 2003 and September 2006. Results. Of the 62 patients with open tibial fractures who were identified in our initial search, 40 had fractures that met our inclusion criteria as type III diaphyseal tibial fractures. Three patients were excluded because their fractures were managed with early limb amputation, and 2 were excluded because of incomplete follow-up records. Twenty-seven of these 35 patients had at least 1 organism present in initial deep-wound cultures that were performed at admission to the hospital. The pathogens that were identified most frequently were Acinetobacter, Enterobacter species, and Pseudomonas aeruginosa. Thirteen of the 35 patients had union times of >9 months that appeared to be associated with infection. None of the gram-negative bacteria identified in the initial wound cultures were recovered again at the time of a second operation; however, all patients had at least 1 staphylococcal organism. One patient had an organism present during initial culture and in the nonunion wound; this organisim was a methicillin-resistant Staphylococcus aureus strain that was inadvertently not treated. Five of 35 patients ultimately required limb amputation, with infectious complications cited as the reason for amputation in 4 of these cases. Conclusions. Combat-associated type III tibial fractures are predominantly associated with infections due to gram-negative organisms, and these infections are generally successfully treated. Recurrent infections are predominantly due to staphylococci.