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Objective. To evaluate the influence of exposure to inhaled environmental factors during pregnancy on the diagnosis of juvenile dermatomyositis (DM).Methods. We performed a case-control study comprising 20 juvenile DM patients and 56 healthy controls matched by age and sex who were residents in the metropolitan region of a large city. A questionnaire assessed demographic data and environmental inhalation exposure during pregnancy (occupational exposure to demolition, chalk, construction and/or quarry dust, paints, varnish, gasoline vapor, and/or battery fluids; stationary sources of inhaled pollution near the mother's home; and maternal tobacco exposure). Daily concentrations of inhaled particulate matter, SO 2 , NO 2 , O 3 , and carbon monoxide (CO) were evaluated throughout the gestational period. Results. Maternal occupational exposure to school chalk dust/gasoline vapor in the juvenile DM group was significantly higher compared with controls (50% versus 4.6%; P ‫؍‬ 0.001). Smoking mothers and secondhand smoke exposure at home during pregnancy were significantly higher in the juvenile DM group versus controls (smoking mothers: 20% versus 1.7%; P ‫؍‬ 0.01, and secondhand smoke: 35% versus 19%; P ‫؍‬ 0.07). In univariate logistic regression models, maternal smoking, occupational exposure to inhaled agents, and the highest tertile of tropospheric CO (3.2-5.4 parts per million) in the third trimester were significantly associated with juvenile DM (P < 0.05). In the multivariate analysis, smoking mother (odds ratio [