Pulmonary Langerhans' cell histiocytosis (PLCH) remains an important diagnostic consideration in the differential diagnosis of diffuse infiltrative lung disease, particular among smokers. This review highlights recent progress in our understanding of the etiology, clinical presentation, and diagnostic and therapeutic approaches to this unusual lung disorder. Evolving studies strongly link the basic pathogenesis of PLCH as an uncommon reaction to tobacco smoke. Recent progress in the clinical approach to these patients has emphasized important roles for high-resolution computed tomographic (CT) scanning and immune reactive tissue markers including cluster differentiation (CD) 1a antigen in the diagnosis of this disorder. A rationale diagnostic algorithm and current management strategies are summarized.