In December 2008, pulmonologists at Laval University Hospital notified the Pays de la Loire Interregional Epidemiology Unit of three suspected cases of psittacosis. The patients had attended a bird fair held in late November 2008. An investigation was conducted to characterize the outbreak and identify potential exposure sources among the fair’s participants. A questionnaire examining clinical symptoms, laboratory results, and exposure factors during the fair was sent to the 86 exhibitors and organizers. We identified suspected cases as participants who had a fever or respiratory symptoms in December 2008. We defined a confirmed case as: positive PCR or a fourfold increase in IgG titer (IFA serology) or seroconversion between two blood samples; a probable case as: IgG ≥ 128 or IgM ≥ 16; and a possible case as: IgG [32–64] or stable between two samples or an epidemiological link to a confirmed case. A retrospective cohort study was conducted among exhibitors and organizers. Veterinary and environmental investigations were carried out to identify potential sources of infection. A total of 48 suspected cases were identified: 26 exhibitors, 7 organizers, 9 family members, and 6 visitors. We identified 2 confirmed cases, 2 probable cases, and 44 possible cases. The attack rate among exhibitors/organizers was 38%. There was a significant association between being located in two specific areas of the hall and having psittacosis (RR: 3.64 [95% CI: 1.24–10.72]). Feces samples collected from birds belonging to an exhibitor (possible case) tested positive for Chlamydia by PCR. Ventilation conditions in the exhibition hall were inadequate. Outbreaks of psittacosis following participation in a bird show have rarely been reported. This outbreak was identified through the study on human psittacosis conducted in western France from 2008 to 2009. This investigation led to the formulation of recommendations for the prevention of psittacosis at bird shows, which are held weekly in France. (R.A.)