The purpose of this study is to assess the utility of the chest high-resolution computed tomography (HRCT) scan for estimating the severity of haemoptysis, localize the bleeding site and to determine a cause of the bleeding. We reviewed 80 consecutive patients who were admitted to a respiratory intensive care unit (RICU) for haemoptysis and who underwent unenhanced HRCT scanning and fibre-optic bronchoscopy (FOB) within 48 h. The number and type of lobar involvement on the CT scan were correlated to prognostic factors, the amount of bleeding and the bleeding aetiology. We compared HRCT scan observations on localization and bleeding aetiology with FOB results. The number of involved lobes was correlated with the daily (p<0.001) and cumulative (p<0.001) volume of haemoptysis and found to be significantly greater in the group of patients who were mechanically ventilated and/or died (2.7 vs 1.8, p<0.03). FOB and HRCT localized the bleeding site or side, respectively, in 71 (89%) and 64 (80%) patients (p>0.05). Of the nine patients without FOB localization, HRCT localized the bleeding site in six patients (67%). The initial HRCT scan correctly identified 48 aetiologies (60%), whereas FOB identified only 2 proximal bronchogenic carcinomas. The extent of lobar involvement seen by HRCT is a prognostic factor correlated with the daily and cumulative volume of haemoptysis. FOB and HRCT are complementary techniques for bleeding site localization. HRCT-scan is also the best exam to determine the cause of haemoptysis, even while it is occurring.