PURPOSE: To correlate high-resolution CT (HRCT) findings with smoking history and pulmonary function test (PFT) in patients with idiopathic pulmonary fibrosis (IPF) with or without coexisting emphysema. MATERIALS AND METHODS: The study included 24 patients who had undergone HRCT and in whom IPF had been confirmed pathologically (n=7) and clinically (n=17). The patients included 19 men and 5 women aged between from 44 and 78 (mean 59) years. HRCT findings were reviewed by two radiologists and assessed for the presence and extent of emphysema (CT emphysema score ; CES) and honeycombing (CT honeycombing score ; CHS). CES and CHS were retrospectively correlated with smoking status and pulmonary function test. RESULTS: Evidence of emphysema was seen on HRCT in 20 of 24 patients with IPF (83 %). CES was 14.3 and CHS was 18.1 in smokers with IPF, as compared with 1.8 and 6.7 in nonsmokers (p < 0.01). Pulmonary function tests showed lower percent predicted FEV1 (69.3 %), FVC (64.7 %), TLC(73.7 %), and RV (77.3 %), a lower percent predicted diffusing capacity of carbon monoxide (58.2%), and normal FEV1/FVC (99.1%). The pulmonary function test in smokers showed higher TLC and RV than in nonsmokers. Eight of nine patients whose CES was higher than their CHS, as seen on HRCT, were smokers and had a smoking history of 33.1 pack-years. Seven of 15 whose CHS was higher than their CES were smokers and had a smoking history of 16.8 pack-years. In patients with a higher CES than CHS pulmonary function test results showed normal TLC (85 %) and RV (100.7%) ; this contrasted with decreased TLC (72 %) and RV (68 %) in patients whose CHS was higher than their CES. CONCLUSION: Emphysema is a frequently associated finding in patients with IPF, as seen on HRCT, and emphysema is more frequent and extensive in smokers with IPF than non-smokers. HRCT is useful for detecting emphysema in patients with IPF, and the extent of emphysema on HRCT correlates with the results of the pulmonary function test and smoking status.