Rationale: IgG4-related disease (IgG4 RD) is a fibro-inflammatory condition that can affect any organ and can lead to the formation of pseudo tumoral lesions requiring differential diagnosis with various malignancies. IgG4 RD can rarely present as an intracranial space occupying lesion. We are reporting a rare case of central nervous system IgG4 RD which presented as seizures with mass lesion. Patient Concerns: A 78-year-old man with bronchial asthma and type 2 diabetes mellitus, well controlled on bronchodilators and oral hypoglycemic agents presented with recurring seizures for 1 month. He gave history of a fall and had sustained a wound over the right forehead. At presentation, he was conscious, oriented, and didn’t have any focal neurological deficits. Diagnosis: Due to the recurring seizures and fall, a contrast enhanced MRI brain was done and was reported as a right temporal space occupying lesion in the lateral sphenoid wing. Meningioma was considered as a possibility and right frontotemporal parietal craniotomy and excision was performed. However, biopsies revealed characteristic findings of IgG4-related disease, including 1) dense lymphoplasmacytic infiltration, 2) fibrosis arranged at least focally in a storiform pattern, and 3) obliterative phlebitis, which confirmed the diagnosis. His IgG4 levels were normal 0.58 g/L [normal range: 0.03 – 2.01 g/L]. Intervention: Patient underwent right frontotemporal parietal craniotomy and excision of mass under general anesthesia. Histopathology was suggestive of IgG4 RD and the patient was started on immunosuppressive therapy including dexamethasone and mycophenolate mofetil. Antiepileptic medications were continued, and he responded to treatment.