Acinetobacter baumannii (AB), an opportunistic pathogen, can cause severe infections, particularly in immunocompromised patients. Naturally resistant to many antibiotics, AB is capable of acquiring resistance mechanisms against carbapenems, including imipenem, leading to treatment challenges. Infections/colonizations caused by imipenem-resistant Acinetobacter baumannii (ABRI) can be reported to the Regional Health Agency and the Coordination Center for the Control of Nosocomial Infections as part of the mandatory reporting system for nosocomial infections (SIN). A retrospective analysis of SIN reports received by the French Institute for Public Health Surveillance between August 1, 2001, and May 31, 2011, shows a marked increase in the annual number of reports for IRAP. Of the 10,288 reports received during this period, 343 (3.3%) involved IRAP. Reports of ABRI accounted for between 2% and 3% of all SINs received from 2003 to 2008, 3.2% in 2009, 5.1% in 2010, and 11.1% in the first five months of 2011. The most frequently reported sites were respiratory infections (37%), bacteremia/sepsis (18.9%), and urinary tract infections (12.6%). The description of two outbreaks in the Nord-Pas-de-Calais region and at the Fort-de-France University Hospital illustrates the methods used for investigation and prevention. (R.A.)