Rationale: Severe and recurrent acute vascular rejection of the pulmonary allograft is an accepted major risk factor for obliterative bronchiolitis. Objectives: We assessed the role of lymphocytic bronchiolitis as a risk factor for bronchiolitis obliterans syndrome and death after lung transplantation. Methods: Retrospective analysis of 341 90-day survivors of lung transplant performed 1995-2005 who underwent 1770 transbronchial lung biopsy procedures. Results: Transbronchial biopsies showed grade B0 (normal) (n=501), B1 (minimal) (n=762), B2 (mild) (n=176), B3 (moderate) (n=70), B4 (severe) (n=4) lymphocytic bronchiolitis and Bx (no bronchiolar tissue) (n=75). 182 transbronchial biopsies were ungraded (8 inadequate, 142 cytomegalovirus, 32 other diagnoses). Lung transplant recipients were grouped by highest B grade prior to diagnosis of bronchiolitis obliterans syndrome: B0 (n=12), B1 (n=166), B2 (n=89) and B3-B4 (n=51). 23 were unclassifiable. Cumulative incidence of bronchiolitis obliterans syndrome and death were dependent on highest B grade (Kaplan-Meier, p<0.001, log-rank). Multivariable Cox proportional hazards analysis showed significant risks for bronchiolitis obliterans syndrome were highest B grade (RR 1.62, CI = 1.31-2.00) (p<0.001), longer ischemic time (RR 1.00, CI 1.00-1.00) (p<0.05) and recent year of transplant (RR 0.93, CI = 0.87-1.00) (p<0.05), while risks for death were bronchiolitis obliterans syndrome as a timedependent covariable (RR 19.10, CI = 11.07-32.96) (p<0.001) and highest B Grade (RR 1.36, CI = 1.07-1.72) (p<0.05). Acute vascular rejection was not a significant risk factor in either model. Conclusion: Severity of lymphocytic bronchiolitis is associated with increased risk of bronchiolitis obliterans syndrome and death after lung transplantation independent of acute vascular rejection.