A 41-year-old man presented with multiple superficial lymph nodes (LNs) swollen with elevated levels of serum immunoglobulin (Ig)G4 and C-reactive protein. Histological findings of his left inguinal LN revealed lymphoplasmacytic infiltration with numerous IgG4-positive plasma cells; IgG4+/IgG+ plasma cell ratio >40%. Chest computed tomography (CT) showed poorly defined centrilobular nodules, interlobular septal thickening, consolidations, and mediastinal LNs swelling. Bronchoalveolar lavage fluid (BALF) showed elevated eosinophils. A surgical lung biopsy showed focal dense eosinophil infiltration, in addition to lymphoplasmacytic infiltration, but few IgG4+ plasma cells. The diagnosis of multicentric Castleman disease (MCD) was made because of serum interleukin-6elevation. Treatment with prednisolone and tocilizumab improved his symptoms and lung lesions. This case shows that overlapping clinical and pathological features of MCD and IgG4-related disease may present in a single patient, showing the difficulty in distinguishing between these two diseases.