Abstract: Military deployment to Southwest Asia and Afghanistan is linked to complex hazardous airborne exposures, but ascertaining the contributions of specific environmental toxicants in causing or contributing to deployment-related distal lung diseases (DDLD) remains challenging. We applied a quantitative microscopy for particulate matter (QM-PM) technique to measure the in situ burden of pigmented and birefringent lung particulates in 24 veterans with DDLD, 10 smokers with respiratory bronchiolitis (RB), and 10 healthy controls. Veterans were more likely to be male (88%) and were significantly younger than RB and healthy controls (mean age 41 vs. 47 vs. 53 years, respectively). Adjusting for age, the anthracotic pigment fraction in lung tissue from DDLD was similar to RB (1.69% vs. 1.37%, P = 0.72), and was significantly greater than healthy controls (0.52%, P = 0.02). Pigment fraction in veterans was significantly associated with higher reported burn pit smoke exposure (P = 0.02), but not sandstorms or diesel exhaust. Birefringent dust density, indicating retained silica/silicates, was significantly increased in RB (28.89/mm2, P < 0.01) compared to DDLD and healthy control groups (8.93 and 9.44/mm2). Findings suggest that lung deposition of anthracotic dust from burn pit smoke exposure in previously deployed post-9/11 military veterans may be important in the pathogenesis of DDLD.