OBJECTIVE To retrospectively quantify the change in the diagnosis and management of suspected interstitial lung disease when thin-section computed tomography (CT) is added to pretest probabilities. METHODS The institutional review board does not require approval or patient informed consent for retrospective study of case records and CT studies. Six pulmonologists reviewed data sheets containing clinical information and results of pulmonary function tests and chest radiographs of 168 consecutive patients (86 women and 82 men; mean age, 59.8 years; age range, 22-86 years) suspected of having interstitial lung disease. Differential diagnoses and responses to specific questions regarding patient care were recorded before and after assimilation of thin-section CT findings. Both unweighted and weighted kappa analyses were used to determine agreement between pulmonologists before and after CT. RESULTS First-choice diagnosis changed in 520 (51%) of 1008 cases, and agreement on first-choice diagnosis increased from 0.47 to 0.72 after thin-section CT. In addition, confidence in the first-choice diagnosis increased, and there was a reduction in the number of differential diagnoses offered by all pulmonologists (P < .005 and P < .001, respectively). Agreement on diagnostic probabilities for individual disorders increased substantially, particularly for diagnoses of idiopathic pulmonary fibrosis (weighted kappa = 0.58-0.89). With CT findings, pulmonologists changed their pre-CT responses regarding the use of bronchoalveolar lavage, transbronchial biopsy, and thoracoscopic biopsy in 242 (24.0%), 282 (28.0%), and 292 (29.0%) of 1008 cases, respectively. However, agreement for the use of these investigations was low both before and after CT. The request rate for thoracoscopic biopsy in patients in whom idiopathic fibrosis was diagnosed decreased from 48 of 179 (26.8%) to 26 of 233 (11.2%) after CT. CONCLUSIONS Thin-section CT resulted in a change in first-choice diagnosis in half the cases. Diagnostic confidence improved, and CT findings increased agreement between pulmonologists on diagnostic probabilities across a range of interstitial lung diseases.