A Bhutanese woman living as a refugee in Nepal immigrated to the United States. She developed progressive dyspnea over 3 years and cough productive of blood-streaked sputum over the month prior to presentation. A chest radiograph performed during an immigration-related medical examination was abnormal. Subsequent high-resolution CT imaging showed bilateral tiny centrilobular upper lobe ground-glass nodules (Fig 1). Sputum was negative for acid-fast bacteria, with no growth of mycobacteria for 56 days, but a polymerase chain reaction assay was positive for atypical mycobacteria. Repeat CT scan 6 weeks later showed increasing profusion of nodules and hilar lymphadenopathy (Fig 2), prompting referral. She denied fever, chills, weight loss, and night sweats. She was a never-smoker and was a homemaker. Physical examination was normal. Pulmonary function tests showed FEV1 of 1.22 L (67%), FVC of 1.93 L (81%), and FEV1:FVC ratio of 63%, with total lung capacity of 3.29 L (95%) and a diffusing capacity of the lung for carbon monoxide of 10.1 mL/mm Hg/min (55%), suggesting mild obstruction with normal lung volumes and moderate reduction of diffusion capacity. The differential diagnosis included sarcoidosis, pulmonary Langerhans cell histiocytosis, and inflammatory bronchiolitis (possibly mycobacterial). Bronchoscopy was performed. The CD4:CD8 ratio in BAL fluid was 1:1, and cytology showed numerous dust-filled macrophages (Fig 3). Transbronchial biopsy showed heavy deposition of black dust within the interstitium accompanied by mild interstitial fibrosis. With polarized light, the black dust was nonbirefringent, but smaller numbers of admixed particles were strongly birefringent (consistent with silicates) or weakly birefringent (consistent with crystalline silica) (Fig 3). There were no granulomas or silicotic nodules. SEM/EDS analysis of the tissue7 revealed many more inorganic particles than were apparent using polarized light (Fig 4). Particle types identified were carbonaceous particles, silica, aluminum silicates, and a few metallic particles containing iron or titanium.