Rational:Cause of bronchiectasis remains undetermined in half of the patients. BPI (Bactericidal Permeability Increasing Protein)-ANCAs could be involved in its pathogenesis.Method: We screened BPI-ANCAs in sera from patients with « idiopathic » diffuse bronchiectasis without vasculitis sign.Results: Thirteen patients with bronchiectasis associated to BPI-ANCAs (BAA) were compared to 26 control patients with diffuse bronchiectasis without ANCA. The sex ratio man/woman was 7/6 in the BAA group versus 2/24 in the control group (p=0,001); BAA group experienced more severe general condition with loss of weight for 77% versus 8% in ANCA-free group (p<0,0001). Almost 54% patients reported asthenia (versus 8%; p<0,001). Gram-negative bacteria colonization was found in 92% of the BAA group versus 50% in the control-one (p=0,009), including Pseudomonas Aeruginosa (p=0,008) and E. Coli (p=0,003). No difference was seen in exacerbation (EA) rate. Obstructive ventilatory disorder was more severe in BAA group (p=0.008). Despite adaptated antibiotherapy, 6 BAA-patients worsened their respiratory function with an altered general condition or got incontrollable recurrent hemoptysis. Immunosuppressive treatment was administrated (prednisolone plus cyclophosphamide), which allowed improvement. Two non-treated patients died from respiratory insufficiency and cachexia. No pulmonary vasculitis was identified on histology available in one patient.Conclusion: The particularities at diagnostic (severity, evolution) and the response to immunosuppressive treatment in BAA group justify to further evaluate the systematic search of BPI-ANCAs in patients with diffuse bronchiectasis.