Gefitinib (Iressatrade mark) is an epidermal growth factor receptor tyrosine kinase inhibitor that has been approved for the treatment of lung cancer in Japan, however, after marketing several cases of severe pulmonary toxicity were reported. The West Japan Thoracic Oncology Group conducted an independent survey of acute pulmonary toxicity and interstitial lung disease (ILD) caused by gefitinib in its member's institutions. The purpose of this study was to clarify the image characteristics of ILD caused by the molecular-targeting drug gefitinib. A total of 1976 patients had been treated with gefitinib between August and December 2002, and 102 of them were suspected of having acute pulmonary toxicity and ILD. A final definite diagnosis of gefitinib-induced ILD was made by at least three radiologists based on a review and analysis of the chest radiography and CT findings plus the clinical data in the medical records. The imaging findings were classified into four patterns: (A) a nonspecific area with ground-glass attenuation, (B) a multifocal area of airspace consolidations, (C) patchy distribution of ground-glass attenuation accompanied by interlobar septal thickening, and (D) extensive bilateral ground-glass attenuation or airspace consolidations with traction bronchiectasis. CT as well as chest radiography had been performed in 65 of the 102 patients at the onset of ILD, and chest radiography alone had been performed in 26. After excluding 11 cases with insufficient data and 21 cases concluded to be other pulmonary diseases, 70 patients were diagnosed with gefitinib-induced ILD. Finally, the diagnostic image findings were classified as pattern A in 29 cases, pattern B in 7 cases, pattern C in 3 cases, pattern D in 20 cases and others in 11 cases. The CT images were classified as pattern A, B, C, and D in 24, 7, 1, and 12 cases, respectively. The mortality rate was significantly higher in the patients with pattern D than the other patterns. Pattern D were thought to represent the features of diffuse alveolar damage. In conclusion, the molecular-targeting drug gefitinib induces pulmonary toxicity at a certain rate and the imaging findings of ILD induced by gefitinib are similar to those of pulmonary toxicity induced by conventional antineoplastic agents.