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To characterize the descriptive and molecular epidemiology of Acinetobacter baumannii in our hospital.Longitudinal analysis of electronic microbiology laboratory records and isolates.A 1,500 bed public teaching hospital in the Miami area.Consecutive patients with A. baumannii from January 1994 to December 2011.NoneData on all A. baumannii isolates were clustered at the patient level, and the first isolate per single patient was determined. Yearly trends were analyzed based on carbapenem susceptibilities and originating units for all first isolates and first blood isolates per unique patient. Additionally, carbapenem nonsusceptible isolates frozen in the microbiology laboratory since 1998 were retrieved and evaluated using polymerase chain reaction and randomly amplified polymorphic DNA techniques. A total of 9,334 A. baumannii isolates were detected, of which 4,484 isolates (48%) were identified as first positive isolates per unique patient. Most of the burden of disease was located in the ICUs (odds ratio, 2.64 [95% CI, 2.17–3.22]; p < 0.0001) and in the adult wards (odds ratio, 3.867 [95% CI, 2.71–5.52]; p < 0.0001). Respiratory specimens constituted the most frequent source (49%; odds ratio, 1.619 [95% CI, 1.391–1.884]; p < 0.0001). Of the 4,484 first isolates, 846 isolates (18.9%) were carbapenem nonsusceptible and 3,638 isolates (81.1%) were carbapenem susceptible. Over the years, the number of carbapenem nonsusceptible isolates increased, whereas the number of carbapenem susceptible decreased (p < 0.0001). The trauma ICU had the highest burden of carbapenem nonsusceptible first isolates (205 of 846; 24.2%). Seven clones were discovered among 144 carbapenem nonsusceptible isolates; one of these clones was found from 1999 to 2005. OXA-23 and OXA-40 were identified in 96 and 13 isolates, respectively. One isolate harbored a novel CTX-M-115 enzyme.This constitutes the largest experience with A. baumannii reported to date from a single center. Half of all isolates were respiratory specimens and were from adult ICUs, especially trauma. Even though this was a polyclonal process, a single clone was identified in the hospital through a 6-year span.