The molecular epidemiology and the genetic basis of antibiotic resistance in 88 multidrug-resistant (MDR) Acinetobacter baumannii strains isolated during 18 months from infected patients in seven intensive care units (ICUs) in Rome were investigated. Random amplified polymorphic DNA and macrorestriction analysis identified two predominant clonal types, genetically related to the European epidemic clones I (type 2) and II (type 1), accounting for 98.9% of A. baumannii ICU isolates. Type 1 was isolated from all ICUs under survey. Class 1 integrons of 2.2 and 2.5 kb were detected in type 1 and type 2 isolates, respectively. The integron structures were similar to those previously determined for epidemic A. baumannii strains from various European countries, and suggestive of integron rearrangement/exchange among isolates related to the European epidemic clones I and II. Carbapenem resistance was associated with the presence of the bla(OXA-58) gene in type 1 isolates. The results indicate that the A. baumannii type 1 clone has a high potential of spreading among hospitals.