A 34-year-old female smoker had had fatigue, a nonproductive cough, and fevers unresponsive to antibiotics for 3 months. In the 3 weeks before admission, she had night sweats and a weight loss of 6.8 kg. WBC count rose to 1 8,000 without a left shift. Sputum samples yielded only Candida albicans. Skin test with purified protein derivative was negative. A chest radiograph showed preservation of lung volumes with multiple bilateral nodules 1-10 mm in diameter and cysts 5-1 0 mm in diameter (Fig. 1A). A CT scan of the chest confirmed the plain film findings of nodules and small cysts (Fig. 1B). Some nodules had central lucencies. The lung bases and costophrenic angles were not involved on either side. Mediastinal and hilar adenopathy was extensive. Pulmonary function tests showed a mild restrictive abnormality. Findings on transbronchial biopsy of the right upper lobe were nonspecific, butthoracoscopic biopsy ofthe Iingula yielded the diagno515 of pulmonary eosinophilic granuloma (Figs. 1C and 1 D). Eosinophilic granuloma is a form of Langerhans cell histiocytosis that can involve lung and bone in children and young adults. Isolated lung disease is the most common finding in adults. Langerhans cell histiocytosis is characterized by an abnormal proliferation of histiocytes variably mixed with eosinophils, lymphocytes, plasma cells, and neutrophils [1]. In the lung, granulomatous inflammation occurs around bronchioles and arterioles [1]. Eosinophilic granuloma is primarily an interstitial disease, although epithelial destruction may lead to alveolar involvement. Classic radiographic findings in pulmonary eosinophilic granuloma include preserved or increased lung volumes with diffuse cysts and nodules from 1 mm to more than 1 0 mm in diameter, more common in the upper lobes and not involving the costophrenic angles [2-4]. High-resolution CT is superior to plain films for initial diagnosis, as nodules and cysts are more clearly defined [5]. Early in the disease, nodules predominate whereas cysts become more numerous later on [5]. Adenopathy is rare in adults, but it may be seen more commonly in children [2]. Spontaneous pneumothorax is identified at presentation in up to 20% of cases [2]. Pleural effusions are rare [4]. Advanced cases may be characterized by pulmonary fibrosis. Clinical and radiologic findings are often discordant [1]. Approximately 30% of patients with pulmonary eosinophilic granuloma have constitutional signs and symptoms, but up to 25% are asymptomatic [2]. The most common sign is a nonproductive cough [2]. Physical examination is often unrevealing. The disease is most common in the third and fourth decades [1]. At least 90% of cases are associated with smoking [2]. No other environmental exposures have been implicated. Results of pulmonary function tests are nonspecific and may show a mixed pattern with obstructive and restrictive components [2]. Pulmonary eosinophilic granuioma can be diagnosed with transbronchial biopsy or bronchoalveolar lavage, but definitive diagnosis often requires open or thoracoscopic lung biopsy. Patients with pulmonary eosinophilic granuloma usually have a favorable prognosis with a high rate of spontaneous remission [2, 4]. Smoking cessation is the first line of treatment; corticosteroids are added if the disease progresses. In some cases, cytotoxic drugs have been used with mixed success. Pleurodesis may be necessary for recurrent pneumothoraces.