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To determine the frequency of cystic lesions on high-resolution computed tomography (CT) in patients with subacute hypersensitivity pneumonitis.High-resolution CT scans in 182 patients with proven subacute hypersensitivity pneumonitis were retrospectively evaluated for the presence of lung cysts. Patients with CT evidence of emphysema or interstitial fibrosis and patients with connective tissue disease were excluded from the study. Two thoracic radiologists reviewed the thoracic CT scans for the presence and location of lung cysts.Thin-walled lung cysts were identified in 24 (13%) of 182 patients and ranged in size from 3 to 25 mm in maximal diameter. The patients included 16 men and 8 women (age range, 30–79 years; mean age, 48 years). The cysts ranged from 1 to 15 in number (mean, 4 cysts) and had a random distribution. Sixteen of the 24 patients also had areas of decreased attenuation and vascularity consistent with air trapping.Thin-walled cysts can be seen in a small percentage of patients with subacute hypersensitivity pneumonitis. The cysts resemble those seen in lymphocytic interstitial pneumonia, and their pathogenesis is uncertain.