In early February 2007, the coordinating physician at a nursing home reported a significant number of flu-like illnesses among residents and staff. An investigation was then conducted to confirm and describe the outbreak, identify factors associated with the illness, and quickly recommend measures to control the outbreak. A cohort study was conducted among all residents and staff. Demographic, geographic, and medical information was collected from medical records or through the administration. A descriptive analysis of the outbreak was performed, and the association between various factors and the illness was estimated using relative risks and their 95% confidence intervals. The etiology of influenza was confirmed by rapid tests. Of 89 residents and 54 caregivers, 43 residents (48%) and 14 caregivers (26%) were cases, 2 of whom were biologically confirmed. Influenza vaccination coverage among residents was 65%. No staff members were vaccinated. The attack rate was three times higher in one of the two living areas, which was affected first and housed more vulnerable residents. The description of the epidemic curve suggests that facility staff may have contributed to the transmission of the virus, particularly from one building to another. The outbreak was not reported to the authorities until the 9th day, when the first control measures were implemented. Incomplete vaccination of residents and staff, the possible role of staff in virus transmission, the delay in reporting and implementing initial control measures, and the proximity of vulnerable individuals in a communal setting likely contributed to the emergence and spread of the outbreak, underscoring the importance of adhering to existing guidelines. Facilities must organize themselves for the prevention, identification, reporting, and management of this type of event, particularly through the regular presence of a coordinating physician and the training of other staff members. (R.A.)