The purpose of this study is to assess the differences of high-resolution CT (HRCT) findings in patients with idiopathic pulmonary fibrosis (IPF) and pulmonary involvement of collagen vascular disease (CVD). We analyzed the HRCT findings of 33 patients with IPF and 23 patients with CVD in terms of predominant pattern, site of involvement, mediastinal lymph node enlargement, pleural change, and pulmonary volume loss. The predominant HRCT pattern was honeycombing for IPF (58%), and ground-glass opacity for CVD (57%). Predominantly subpleural involvement was seen in 90% of IPF and 83% of CVD patients. Mediastinal lymph node enlargement was seen in 61% of the patients with IPF and 13% with CVD (p = 0.0004). Pleural thickening was seen in 97% of the patients with IPF and 35% with CVD and the severity of pleural thickening is statistically significant (p = 0.00001). Pleural effusion was seen in 6% of the patients with IPF and 26% with CVD (p = 0.0351). The hilar height ratio was more than 1.5 in 52% of the patients with IPF and 30% with CVD (p = 0.2620). Although HRCT findings of IPF and pulmonary involvement of CVD are similar and overlap considerably, but patients with IPF showed a tendency to more progressed fibrosis than patients with CVD.