Lung involvement is one of the intrathoracic patterns in patients with ISD. Intrathoracic involvement can develop before, during, or after the diagnosis of autoimmune pancreatitis or other extrathoracic lesions in patients with ISD. The most common respiratory symptoms are cough, dyspnea, and chest pain; occasionally, the patient may be asymptomatic. Chest radiographs may show multiple round nodules, alveolar interstitial disease, tracheobronchial stenosis, pleural nodules, or a pleural effusion. Tissue biopsy specimens from lung parenchyma or pleural lesions are useful to differentiate ISD from other diseases with similar radiologic findings, such as lung cancer, lymphoma, or sarcoidosis. Biopsy specimens can be examined to detect the presence of a lymphoplasmacytic infiltrate. In addition, the presence of IgG4-positive lymphoplasmacytic infiltration and an elevated ratio of IgG4/IgG-positive plasma cells in immunohistochemical examinations are helpful to correctly diagnose ISD. Patients with ISD with intrathoracic and extrathoracic manifestations generally respond well clinically to corticosteroid therapy. Steroid response can be seen in 1 to 2 weeks, and the treatment dose must be reduced thereafter.