CASE PRESENTATION: Case 1: A 35-year old Middle Eastern female active smoker with 38 pack-year history presented with six weeks of nonproductive cough. Chest x-ray and computed tomography (CT) demonstrated diffuse bilateral alveolar infiltrates, predominantly in the mid and upper lungs (Figures A and B). Pulmonary function testing (PFT) revealed reduced diffusing capacity for carbon monoxide (DLCO) at 11.1 mL/min/mmHg (47% predicted). Right upper lobe wedge resection confirmed PLCH. The patient committed to smoking cessation. Follow-up at 4, 9, and 41 months showed dramatic decrease in the number and size of nodules on chest x-ray and CT (Figures C and D). PFT returned to near-normal with DLCO 17.0-17.9 mL/min/mmHg (71-76% predicted). Case 2: A 34-year old Caucasian female active smoker with 20 pack-year history presented with two years of dyspnea on exertion and generalized body aches. Chest CT revealed bilateral nodular infiltrates predominantly in the upper and mid lungs (Figure E). Transbronchial biopsy of right upper lobe revealed PLCH. Magnetic resonance imaging of the head, x-ray skeletal survey, peripheral blood flow cytometry, and bone marrow biopsy were normal. Follow-up at 5 and 11 months demonstrated complete resolution of the nodules on chest CT (Figure F).