Introduction - Since June 11, 2009, influenza A(H1N1) 2009 has been classified as a pandemic by the World Health Organization (WHO). The first imported case of 2009 influenza A(H1N1) on Réunion Island, a French overseas department located in the Southern Hemisphere, was diagnosed on July 3, 2009. We describe the characteristics and impact of the epidemic on the activity of an emergency department from the first case through the peak of the epidemic. Methods - Patients presenting to the emergency department with influenza-like illness or symptoms meeting the definition of influenza-like illness were recorded in July and August. Patients with a discharge diagnosis of influenza-like illness were analyzed. Results - Emergency department activity in 2009, compared to 2008, increased by 0.5% in July and 9.7% in August. In July and August, 7.1% and 20.0% of patients with influenza-like illness were hospitalized, respectively. Among the 394 patients studied (186 men, mean age 36.2 ± 18.5 years), 199 (50.5%) had a comorbidity or a risk factor for complications. Complications occurred in 112 patients (28.4%); the most common complications were bronchospasm (52.7%), pneumonia (32.1%), and decompensation of a comorbidity (17.9%). A visit to the emergency department was followed by hospitalization for 73 patients (18.5%). Patients aged 65 and older accounted for 10.9% of the total cohort but constituted 31.5% of those hospitalized and 21.4% of complicated cases. Regardless of age, a comorbidity and/or risk factor was reported in 80.2% of complicated influenza-like illnesses and 86.3% of hospitalized cases. The care pathway for influenza patients was initially centered on a dedicated influenza clinic within the emergency department. This system involved multiple healthcare professionals, disrupted the various departments involved, and was ill-suited for treating children or monitoring patients showing signs of poor tolerance. Even when influenza-like illnesses were identified upon arrival, this system directed patients to different areas of the hospital and different consultation rooms within the emergency department. Conclusion - Recommendations for monitoring, prevention, and referral of individuals with risk factors, particularly respiratory ones, are well-founded. This feedback also raises questions about the patient pathway within a hospital setting and allows for adjustments to organizational plans. (RA)