Rationale:IgG4-related disease is a rare and novel disease entity that tends to involve multiple organs. The pulmonary manifestation of this disease is highly variable and may mimic lung cancer, pneumonia, interstitial lung disease (ILD), sarcoidosis, and so forth. Small airway disease is rarely reported in IgG4-related lung disease (IgG4-RLD). In the current study, we describe a rare case of IgG4-RLD with patterns of ILD and bronchiolitis.Patient concern:A 43-year-old man had chronic cough and dyspnea on exertion for 4 years. Initial chest radiography showed diffuse interstitial infiltration. Follow-up chest computed tomography 4 years later revealed bilateral diffuse centrilobular nodules with tree-in-bud pattern, bronchial wall thickening, and mediastinal lymph nodes. Bilateral diffuse multifocal ground-glass opacities and mosaic attenuation were also observed. Pulmonary function test revealed mixed restrictive and obstructive ventilatory impairment.Diagnoses:Video-assisted thoracoscopic surgery (VATS) lung biopsy showed interstitial fibrosis with lymphoplasmacytic infiltration rich in IgG4-positive plasma cells. Serum IgG4 level also showed remarkable elevation. Therefore, IgG4-RLD is confirmed.Intervention:VATS wedge resection of right upper lobe and mediastinal lymph node.Outcomes:The patient responded well to steroid and immunosuppression therapy, and was regular followed-up in outpatient clinic.Lessons:IgG4-RLD should be considered not only in ILD, but also in small airway disease. Serum IgG4 level may be a useful tool for screening.