Idiopathic pulmonary fibrosis is characterized by an inflammation of the walls of the respiratory airspaces that proceed to fibrotic alveolar derangement. Smoking habits are associated with changes in the number and the activation state of immune and inflammatory alveolar cells. Cigarette smoke could interact with the course of this disease. To evaluate the effects of smoking on IPF, 11 smokers and 16 nonsmokers were compared. Clinical presentation, PFTs, BAL cell populations, short-term glucocorticoid responsiveness and survival were evaluated. Similar PFT results were observed in both groups. Lymphocyte cells were higher in nonsmokers than in smokers. Glucocorticoid responsiveness was mainly observed in nonsmokers. Nonsmoking status was not associated with survival advantage. We conclude that the subset of IPF characterized by an aggressive onset, a BAL fluid high lymphocyte count and a substantial PFT improvement after therapy began, occurs predominantly in the absence of cigarette smoking habits.