PURPOSE: To predict pulmonary arterial hypertension by comparing the extent of honeycombing lesion with the diameter of main pulmonary artery (MPA). MATERIALS AND METHODS: We retrospectively reviewed 21 patients (20 men, one woman) who showed honeycombing lesion on HRCT, and also analysized a control group of 30 (29men, one woman) who had no cardiopulmonary symptom and no abnormality on chest CT. On Chest HRCT, we scanned at four levels [1)aortic arch, 2) bifurcation of bronchus, 3) mid-portion of left ventricle, 4) dome of right diaphragm], and two radiologists then evaluated the proportion of honeycombing lesion within the entire lung field. According to the extent of this, we divided the patients into five groups [<20% (I), 20-39% (II), 40-59% (III), 60-79% (IV), > or = 80% (V)], and then divided Group I into two subgroups [<10 % (I|1), 10-19% (I-2)]. Using contrast-enhanced routine CT, the main pulmonary artery (MPA) was measured at its the widest diameter perpendicular to the long axisat the level of its bifurcation. RESULT: In group I (n=11) MPA was 28.4±2.6mm ; in group II (n=6), it was31.7±2.0mm ; in group III (n=2), 33.5mm ; in group IV (n=1), 33mm ; and in group V (n = 1), 39mm. In subgroup I-1MPA was 26.1±1.9mm, and in subgroup I-2, it was 29.8±1.6mm. In the control group, MPA was 25.1±2.0mm. CONCLUSION: The extent of honeycombing lesion is closely related to the change in diameter of the MPA. Honeycombing lesion extending over more than 10% of the lung field may lead to pulmonary arterial hypertension.