IgG4-related disease (IgG4-RD) is a fibro-inflammatory condition that can affect various organs. Localized sinonasal IgG4-RD is a rare condition characterized by bone and soft-tissue invasion. In this report, we present a case of a patient initially diagnosed with chronic rhinosinusitis, who underwent endoscopic sinus surgery and was later found to have biopsy proven IgG4-related sinonasal disease despite having normal serum levels of IgG4, resulting in erosion of the right lamina papyracea.