Objective. To investigate potential sources of gram-negative multidrug-resistant organisms (MDROs) in a deployed US military healthcare facility. design. Active surveillance. methods. Swab sampling of patients, hospital personnel, and environmental surfaces was performed before the opening of a new medical treatment facility in Iraq and then serially for the next 6 months. Multidrug resistant isolates were genotypically characterized using pulsed-field gel electrophoresis (PFGE). Univariate and multivariate analysis were performed to evaluate associations between patient characteristics and MDRO carriage. setting. Deployed US military medical facility. results. A total of 1,348 samples were obtained, yielding 654 isolates, 42 of which were MDROs. One hundred fifty-eight patients were sampled; swabs from 18 patients yielded 29 MDR isolates. Host nation patients comprised 89% of patients with MDROs and 37% of patients without MDROs (P!.001). Host nation patient status was also significantly associated with MDRO carriage in multivariate logistic regression analysis (adjusted odds ratio, 2.9; confidence interval, 1.3-6.3; P p.009). Bacteria with PFGE patterns matching those recovered from host nation patients were later isolated from environmental surfaces including recovery room patient monitors and the trauma bay floor. conclusions. At this facility, MDRO isolation was predominantly obtained from newly admitted host nation patients, which may reflect baseline colonization with MDROs in the community. Patient MDRO carriage was linked to subsequent environmental contamination. These findings support intensive infection control efforts in forward deployed facilities.