Humidifiers are commonly used in the community to relieve symptoms associated with acute respiratory infections in young children; however, clear benefits of these devices have not been documented. The Environmental Protection Agency has not found any adverse health effects related to humidifier use. We report here the case of a young infant with significant accidental inhalational lung injury related to dispersal of mineral dust from an ultrasonic home-use humidifier. The clinical consequences included prolonged hypoxemia, tachypnea, and failure to thrive. Radiography revealed pneumonitis, and pulmonary-function testing showed a nonreversible mild obstructive ventilatory defect. Because of persistent symptoms, evolution of failure to thrive, and nonresponse to inhaled and short courses of systemic glucocorticoids, an aggressive management approach was successfully pursued with high-dose pulse steroid therapy, which could be a potential therapeutic approach for similar patients. In addition, this case raises important questions about the safety of exposing infants and young children to humidifiers and emphasizes the need for further study.