Multiple bullae have often been observed in the lungs of patients with idiopathic interstitial pneumonia (IIP). The etiology of bullae has been considered to be distinct from that of interstitial pneumonia and honeycomb lesions seen in IIP. The incidence of bullae was evaluated in 27 IIP patients (male; 23 cases, female; 4 cases) and clinical factors which are related to the development of bulla were analyzed. Of the 27 patients, 16 (59%) had bullae. All 16 were male smokers, and had higher smoking indices (p < 0.01) than patients without bullae. Eleven of the 16 IIP patients with bullae had clubbed fingers (69%, p < 0.05). Roentgenologically, cysts (75%, p < 0.05), low attenuation area (56%, p = 0.06), and honeycomb appearance (94%, p = 0.07) were observed more often in IIP patients with bullae. These results suggest that smoking habits may have a close relationship to the development of bullae seen in patients with IIP.