The purpose of this study was to investigate the presence and distribution of integron-carrying isolates among Enterobacteriaceae resistant to β-lactam antibiotics collected from a wastewater effluent of the city of L'Aquila (Italy). A total of 471 Enterobacteriaceae were collected during a period of 2 years (2005-2006). The presence and distribution of class 1 and 2 integrons was investigated by colony blot hybridization using specific probes labelled with dUTP-fluoresceine kit. The variable region of class 1 and 2 integrons was analyzed by polymerase chain reaction and DNA sequencing in 24 isolates with different random amplified polymorphic DNA profile. The characterization of class 1 and 2 integrons gene cassettes of 24 nonrelated strains showed the presence of four different arrays: dfr17-aadA5; aadA10; dfr1-sat1; dfr1-sat1-aadA1. This is the first report from Italy in which the authors confirm the presence of Enterobacteriaceae carrying class 1 and 2 integrons in a wastewater treatment plant that collects the urban and hospital discharges.