SUMMARY. We report a case of a man aged 52 years, smoker, who presented with exacerbation of chronic cough and an abnormality of the right hilum on plain chest X-ray. A computed tomography (CT) scan showed a solid lesion of soft tissue density on the right hilum. Bronchoscopy revealed stenosis of the right medial basal bronchus due to extrinsic compression. Diagnosis was made by surgical removal of the lesion and histological examination. Typical lesions of bronchiolitis obliterans with organizing pneumonia (BOOP) were found. BOOP, either cryptogenic or secondary, presents occasionally as a focal mass, usually at the periphery of the lung, mimicking malignancy. A central location is less usual. Definitive diagnosis requires open lung biopsy. A high index of suspicion allows, in selected cases, closed lung biopsy, steroid treatment and radiological follow up of the lesion. Pneumon 2007; 20(1):87-90.