PURPOSE: To evaluate the HRCT findings of hypersensitive pneumonitis and to correlate the findings with the results of the pulmonary function test (PFT). MATERIALS AND METHODS: Seven patients in whom hypersensitive pneumonitis was histologically confirmed (by transbronchial lung biopsy in two, thoracoscopic lung biopsy in one, open lung biopsy in two, and typical clinical and laboratory findings in two) were involved in this study. Their radiological patterns were assessed by HRCT and the extent of each finding was evaluated semi-quantitatively and correlated with the results of the pulmonary function test. RESULTS: The HRCT findings were as follows: lobular overinflation (n = 7), ground glass attenuation (n = 7), centrilobular nodule (n = 6), reticular opacity (n = 5), interlobular septal thickening (n = 3), consolidation (n = 2), and irregular subpleural line (n = 1). Five patients showed lower lung predominance and two, middle lung predominance. In all, a restrictive pattern and diminished diffusion capacity was noted. The grade score of reticular opacity showed significant correlation with forced vital capacity and forced expiratory volume. There was, however, no significant correlation between other HRCT findings and PFT results. Two patientsin whom lobular overinflation associated with parenchymal fibrosis was noted showed a decreased maximal midexpiratory flow rate of 25 -75. CONCLUSION: Lobular overinflation, ground-glass attenuation and centrilobular nodules are commonly observed in hypersensitive pneumonitis. The only significant correlation between each HRCT finding and the pulmonary function test was that between reticular opacity and both forced expiratory volume and forced vital capacity. In cases of chronic hypersensitive pneumonitis presenting as pulmonary fibrosis, associated lobular overinflation could be helpful for differential diagnosis.