Purpose : To determine the CT factors which predict positive results of bronchoscopic biopsy in cases of lungcancer with CT-bronchus sign. Materials and Methods : In 30 patients who on CT showed a lung mass with CT-bronchussign and who had undergone bronchoscopic biopsy, lung cancer was confirmed histopathologically and/or clinically.The CT findings were evaluated for the location, nature and size of the mass, and the type of CT-bronchus sign, and the diagnostic rate of bronchoscopic biopsy and of CT findings was compared. Results : Seventeen of 30patients(56.7%) were diagnosed by bronchoscopic biopsy and their diagnostic rates according to the location wereas follows:100%(10/10) in cases involving the lobar bronchus; 60%(6/10) in cases involving the proximal segmentalbronchus and 10%(1/10) in cases involving the distal segmental bronchus. In 20 cases of peripheral lung cancer, 16.7%(1/6) of masses with less than 3cm in diameter, 44.4%(4/9) of masses with more than 3cm and less than 6cm, and 40.0%(2/5) of masses with more than 6cm were diagnosed bronchoscopically. In addition, 57.1%(4/7) of caseswith abrupt bronchial obstruction, 33.3%(3/9) with a patent bronchus within the mass, 0%(0/3) with bronchialdisplacement or a marginally located bronchus and 0%(0/1) with tapered bronchial obstruction were diagnosed onbronchoscopic biopsy. One of two cases with perilesional lymphangitic spread and two of four cases with a largecavity were diagnosed bronchoscopically. Conclusion : In cases of lung cancer, bronchoscopic biopsy is a usefulinitial diagnostic method where the mass is located in 1cm proximal to segmental bronchial bifurcation and is morethan 3cm in diameter, there is CT-bronchus sign with abrupt bronchial obstruction or a patent bronchus within themass, and associated perilesional lymphangitic spread or large air-cavity. In most cases where there is peripherallung mass less than 3cm in diameter, however, bronchoscopic biopsy alone is not adequate, and the use of a furtherdiagnostic modality is required.