Human chlamydiosis of avian origin (psittacosis) caused by Chlamydophila psittaci was traditionally attributed to pet birds, particularly psittacines. The occurrence over the past decade of several outbreaks in the poultry industry (particularly among turkeys and ducks) and hospitalizations for severe cases necessitate a broader consideration of this risk. Given the likely role of occupational exposure and the potential severity of the disease, the Mutualité sociale agricole, as part of its agricultural zoonosis surveillance network, conducted a seroprevalence survey among poultry industry workers who had taken five days of sick leave in 2000 through its occupational health and medical monitoring services in Brittany and the Pays-de-la-Loire region. This study was driven by several observations: - lack of an organized information system to assess the frequency of the disease (excluding hospitalized cases); - difficulties in etiological diagnosis due to nonspecific symptoms; - underreporting of occupational diseases (a few cases per year); - lack of evaluation of individual or collective preventive measures.