Immunoglobulin G4 (IgG4)-related disease is a recently described autoimmune disease that can involve diverse organ systems, causing pancreatitis, cholangitis, retroperitoneal fibrosis, and thyroiditis to name a few. Key histological features include storiform fibrosis, obliterative venulitis, and intense inflammatory infiltrate composed of lymphoplasmacytic cells. The disease has a tendency to present with mass-forming lesions, often difficult to differentiate from malignant processes. We report the case of a 48-year-old male from an area endemic for gallbladder cancer (north India). He presented with a short history of abdominal pain and was found to have asymmetric thickening of the gallbladder wall with a soft-tissue mass invading the adjacent liver. In addition, the bile duct was dilated throughout its extent. A clinical and radiological diagnosis of gallbladder cancer with choledochal cyst was made, and the patient underwent radical cholecystectomy with bile duct excision. Histopathology surprisingly demonstrated IgG4-related disease with no evidence of malignancy. Notably, serum levels of immunoglobulins were found to be normal. Preoperative diagnosis was challenging due to the absence of other manifestations. IgG4-related disease is a possible diagnostic pitfall and should be included as a possible differential diagnosis for gallbladder masses.