SUMMARY Over the last decade, Acinetobacter baumannii resistant to carbapenems has emerged in many medical centres and is commonly associated with high morbidity and mortality. We investigated potential mechanisms contributing to antimicrobial resistance of 58 clinical isolates of A. baumannii collected during a prolonged city-wide outbreak in five different hospitals in southern Brazil. The integrase gene was detected in 51 (87·9%) isolates of which 36 harboured class 2 integrons alone and 14 had both class 1 and 2 integrons; all carbapenem-resistant isolates displayed class 2 integrons. ISAba1 was found upstream of bla OXA-23-like only in isolates resistant to carbapenems; however, ISAba1 upstream of blaOXA-51-like was present in both susceptible and resistant isolates. This is the first report of a high prevalence of class 2 integrons in A. baumannii in southern Brazil. Moreover, our study suggests that ISAba1/blaOXA-51-like alone is insufficient to confer resistance to carbapenems.