Background: Legionnaires' disease is a severe form of pneumonia, and although public health medical inspectors must be notified, it is often under-reported. The objectives of this study were to determine the completeness rate of notification of Legionnaires' disease and to estimate the incidence of this disease in Wallonia, the southern part of Belgium, in 2012.Method: This retrospective, transversal descriptive study was based on a capture-recapture method using two sources. An estimation of the total number of Legionnaires' disease cases was calculated using Chapman and Seber's estimators for small numbers, thereby allowing us to estimate the real incidence of this disease in Wallonia as well as the completeness rate of notification.Results: The total number of estimatedLegionellacases for 2012 was 45 (IC 95%:41-48) and the completeness rate was 65% (IC 95%:61-70%). The estimated incidence of Legionnaires' disease in Wallonia was 1.27/100,000 inhabitants.Conclusions: The notification rate ofLegionellamust be improved in Wallonia. Doctors should be made aware of the importance of diagnosing and reporting Legionnaires' disease. ; SCOPUS: ar.j ; info:eu-repo/semantics/published