We report a case of immunoglobulin G4 (IgG4)-related lung disease presenting as a solitary pulmonary nodule with an irregular margin on computed tomography. The nodule showed a high standardized uptake value on positron emission tomography. A malignant pulmonary tumour could not be excluded. Middle lobectomy was performed. Histological analysis revealed marked lymphoplasmacytic infiltration and storiform fibrosis. Immunostaining indicated the presence of IgG4-positive plasma cells. A definitive diagnosis of IgG4-related disease was confirmed.