A prospective survey of sputum cytologic specimen was performed for 16 months from Jan. 1993 to Apr. 1994 in Presbyterian Medical Center. The purpose of this study is to find the positive rate of sputum cytology in the diagnosis of lung cancer and to correlate these results with tumor location and stage. Sputum cytologic specimen were received from 104 patients among 158 patients diagnosed as lung malignancy by histologic examination. Cytologic diagnosis of "suggestive of malignancy" was made in 61 patients (59%) and dysplasia in 9 patients(9%), atypia in 14 patients(13%), benign in 15 patients(14%) and inadequate specimen in 5 patients (5%), respectively. Among 84 patients beyond the cytologic diagnosis of atypia, 51 patients (61%) disclosed a central location, while 33 patients (39%) showed peripheral lesions. All 54 patients diagnosed as suggestive of non-small cell carcinoma were stage III or over, and all 7 patients diagnosed as suggestive of small cell carcinoma were in advanced stage. These results suggest that the cytologic examination of sputum seems to be an important tool in diagnosis of lung cancer.