A 73-year-old male was admitted to Rakuwakai Otowa Hospital because of increasing dyspnea on exertion and skin eruption. His past history was unremarkable except for hypertension. Through radiographic examination revealed diffused and patchy ground-glass opacity, prominent hilar shadow, a small amount of bilateral pleural effusion in the chest, and mucosal thickening in the paranasal sinuses. A laboratory examination showed eosinophilia (4,260/μl, 49% leucocytes), positive CRP (6.3 mg/ml), hypoalbuminemia (2.9 g/dl), and elevated serum IgG (3,013 mg/ml), IgG4 (966 mg/ml), and IgE (544 IU/ml). Autoantibodies were negative. A 12% (230 ml) increase of FEV_1.0 and a decrease of respiratory system impedance (Zrs) were observed after use of a bronchodilator. A fiberoptic bronchoscopy revealed white-yellow plaque on the tracheal and bronchial walls. Biopsies of the lung and tracheal lesion showed IgG4-positive plasma cell infiltration with a few eosinophils in the alveoli and eosinophil infiltration with a few IgG4-positive plasma cells in the tracheal plaque. A biopsy of the skin eruption showed an infiltration of eosinophils, neutrophils, and histiocytes and a few IgG4-positive plasma cells. A diagnosis of Churg-Strauss syndrome (CSS) was made. This case also fulfilled the criteria of IgG4-related diseases. Corticosteroid therapy was started, and the skin eruption subsided rapidly and almost disappeared. The eosinophil count in peripheral blood was normalized within a month, and it took a few more months for serum IgG4 to do the same. The observed difference in the infiltration of IgG4-positive plasma cells and eosinophils in the involved tissues may influence the clinical symptoms of CSS and coexisting IgG4-related lung diseases.