Introduction. Regionalized surveillance of severe cases of influenza A(H1N1)2009 requiring admission to intensive care units was implemented in the Provence-Alpes-Côte d'Azur (PACA) and Corsica regions effective November 16, 2009. Following the epidemic, a survey was conducted to assess the completeness of reports of severe cases and to discuss the value of a sentinel surveillance system. Method. On November 24, 2009, the Cire sent a letter to all heads of intensive care units to raise awareness about reporting severe cases. Follow-up on these cases was conducted via weekly telephone contact with the reporting units. In January 2010, units that had not reported any cases were contacted to determine whether they were capable of admitting severe influenza cases and to ascertain the number of cases admitted to their units. Results. Of the 91 units identified and contacted, 55 were capable of admitting severe influenza cases. One hundred and five cases had been reported by 30 units (26 hospitals). The survey identified ten previously unreported cases in five other units. The completeness of reporting was estimated at 90%. Hospitals in major metropolitan areas (14 facilities) admitted the most severe cases, accounting for 75% of cases (85 cases). These cases were representative of the overall population in terms of age, sex, severity, and temporal distribution. Discussion/Conclusion. Coordinating surveillance at the regional level facilitated the development of a new network of partners. There was high engagement among intensive care physicians, ensuring good coverage of the surveillance system. The study shows that the system is adaptable to surveillance objectives. Thus, a system limited to sentinel units would have allowed for trend monitoring and case characterization. (R.A.)