Introduction - Beginning in August 2004, hospitals within the Assistance publique-Hôpitaux de Paris (AP-HP) system faced repeated outbreaks of glycopeptide-resistant Enterococcus faecium (ERG). Objective - To describe the impact of enhanced control measures on ERG outbreaks in AP-HP hospitals. Materials and Methods - A prospective registry of each new ERG case was established in AP-HP hospitals. In response to an increase in the monthly number of new cases, enhanced control measures were implemented for each new outbreak occurring from January 2006 onward. These measures included the rapid mobilization of the affected hospital teams, the suspension of transfers of cases and contacts to other hospital departments, repeated screening of contact patients, and the grouping of cases, contacts, and new admissions into three separate areas. The impact was measured by changes in the number of cases, the average number of cases per outbreak, and the average duration of outbreaks. Results - Between August 2004 and December 2007, 23 ERG outbreaks occurred in 12 AP-HP hospitals, involving a total of 379 identified patients (61 infections and 318 colonizations). Before and after January 2006, the median number of cases per outbreak was 9 (range 3 to 112) and 5 (range 2 to 16), respectively; and the median duration of the outbreaks was 2.1 months (range 0.2 to 29.8) and 1.4 months (range 0.4 to 3.9), respectively. Conclusion - It is possible to control ERG outbreaks provided that a very rapid response is ensured within healthcare facilities and patient transfers are limited to prevent the spread of ERG. (R.A.)