Cigarette smoking is a common cause of lung disease. It is clearly implicated in the development of chronic obstructive pulmonary disease and lung cancer. Importantly, cigarette smoking has also been implicated in the development of interstitial lung diseases such as respiratory bronchiolitis interstitial lung disease, desquamative interstitial pneumonia, pulmonary Langerhans' cell histiocytosis,and idiopathic pulmonary fibrosis. The exact role of cigarette smoking in the development of interstitial lung diseases is still being defined; the relatively low prevalence of interstitial lung disease makes epidemiologic studies difficult.