Introduction - An initial cluster of influenza A(H1N1)2009 cases among healthcare workers was reported at the Limoges University Hospital in August 2009. Methodology - An epidemiological investigation involving active case finding was conducted. Epidemiological and clinical data were collected during structured interviews. Testing for the influenza A(H1N1)2009 virus was performed using RT-PCR (Reverse Transcriptase-Polymerase Chain Reaction). A specific questionnaire was used to identify the transmission prevention measures implemented in the affected departments. Results - The investigation identified 9 suspected cases of influenza among healthcare staff in eight departments of the university hospital: 4 were classified as confirmed, 2 as probable, and 3 as possible. A link between the first 4 cases was identified, whereas no epidemiological link was found with the last 5 cases, suggesting a possible second chain of transmission. Secondary prevention measures, rapidly implemented within the affected departments, included, in particular, the wearing of masks at the first sign of symptoms and exclusion from work as soon as symptoms were reported. Discussion - The absence of transmission to patients and the limited transmission to staff working in the same department underscore the importance of strengthening individual and collective prevention measures throughout the hospital shortly after the first case of influenza is reported. (R.A.)