Background: Bronchiolitis obliterans organizing pneumonia ( BOOP) may be classified as cryptogenic ( idiopathic) and secondary. There are no clear clinical and radiological features distinguishing between idiopathic and secondary BOOP. Objectives: To analyze the etiologic factors, clinical and radiological features, diagnostic approach and response to therapy at onset and outcome in subjects with BOOP. Methods: The medical files of Erciyes University Hospital from 1995 to 2003 were retrospectively reviewed. Patients with biopsy-proven BOOP were selected for evaluation. The etiology and initial features of BOOP, treatment, resolution, relapse, and survival were obtained from medical records, and a follow-up patient questionnaire. Results: We have diagnosed 26 cases ( 13 males / 13 females) with BOOP syndrome (mean age 54 +/- 15 years, range 14 - 93). More than half the patients (58%) were classified as idiopathic BOOP. Patients presented with cough (92%), dyspnea (70%), pleuritic chest pain, hemoptysis and fever (50%). The biopsy specimens had been obtained by transbronchial and/or transthoracic lung biopsy in 18 cases (69%). At radiological evaluation, there were bilateral patchy alveolar and/or interstitial infiltrates in 16 patients (62%), and solitary pneumonic involvement in 10 patients (38%). Three patients recovered spontaneously, 5 remained cured after resection of the focal lesion. Corticosteroid therapy was given in 17 patients (65%). Apart from four patients who died ( death was attributable to BOOP in only 1 patient) and three patients who relapsed, the prognosis was good in all patients. Conclusions: The etiology of BOOP is usually idiopathic. We observed that hemoptysis and pleuritic chest pain were a relatively frequent symptom in BOOP in the present series, in contrast to previous observations. The diversity of radiological and clinical presentations including hemotysis and pleuritic chest pain should prompt consideration of the diagnosis in patients with persisting pulmonary symptoms and radiological findings. Copyright (C) 2005 S. Karger AG, Basel.