Background: Regional Health Agencies (ARS) receive reports of adverse events related to patient care within the healthcare and medico-social services system, which are submitted to them by healthcare facilities and professionals. Some of these events constitute serious adverse events (SAEs, events resulting in the patient’s death, a life-threatening condition, hospitalization, prolonged hospitalization, or the occurrence of sequelae). The main objective of this study was to describe the characteristics of SAE reports received in 2012 and 2013 by the Île-de-France Regional Health Agency (ARSIdF) and to analyze trends between these two years. Materials and Methods: The analysis covered all serious adverse events reported to the ARSIdF during the period from January 2012 to December 2013. The reports originated from healthcare and medical-social facilities. User complaints were also taken into account. The variables analyzed were: the category of the reporting entity, the time to reporting to the ARSIdF, any link to a regulated vigilance system, the patient’s age and sex, and the severity of the event. Results: Of the 883 reports of adverse events related to care collected during the study period, 270 met the definition of a serious adverse event (SAE) and were included in the analysis. One-third of these were suicidal behaviors (N=89, 33%). The increase in the number of reports between 2012 and 2013 was significant (+31%, p=0.03). The data came from both the healthcare sector (n=185, 69%) and the medical-social sector (n=85, 31%). The reporting delay exceeded 15 days in one-quarter of cases. The distribution of reports by severity was significantly different from that obtained in the national ENEIS surveys (p<10⁻⁴). Discussion Conclusion: This descriptive study presents, for the first time, the characteristics of adverse events spontaneously reported to the ARSIdF, with a significant proportion of reports originating from medical-social institutions. The study nevertheless excludes healthcare-associated infections. It highlights significant underreporting, which primarily concerns the least severe events. Efforts to promote a culture of reporting and risk management should be strengthened.