We examined the chest CT results of 27 cases of drug-induced pneumonitis. We classified the subjects into 3 groups in accordance with the clinicopathological findings: eosinophilic pneumonia (EP) group (5 cases), diffuse alveolar damage (DAD) group (3 cases), and interstitial pneumonia (IP) group (19 cases). We evaluated the CT findings in each group, and made a further subclassification. In the EP group, the CT findings were subdivided into two, namely, type A, with diffuse distribution consistent with CT finfings of acute eosinophilic pneumonia; and type B, with subpleural distribution consistent with chronic eosinophilic pneumonia. In the DAD group, the CT findings were diffuse distribution of mixed ground-glass attenuation and air-space consolidation, with or without traction bronchiectasis, and without shrinking of the lung. In the IP group, the CT findings were subdivided into 3, namely type A, with ground-glass attenuation dominant, without traction bronchiectasis or shrinking of the lung, consintent with the CT findings of IP without fibrosis; type B, with air-space consolidation dominant, with traction bronchiectasis and shrinking of the lung, consistent with the CT findings of IP with fibrosis; and type C with multiple nodules dominant. Radiological differentiation of the DAD group from IP-type B may be possible by the presence or absence of a shrinking lung pattern. We concluded that the subgroups of CT findings in drug-induced pneumonitis may be useful for diagnosis of this disease, and for prognosis.