This report describes a unique case of IgG4-related disease in a 36-year-old woman who presented with a pelvic mass. Although CT and MR imaging initially suggested a malignant process, further work-up including sigmoidoscopy and surgical exploration revealed no evidence of malignancy. The final pathology indicated an inflammatory process, leading to the diagnosis of IgG4-related disease. After receiving appropriate systemic treatment, the patient\'s symptoms significantly improved. This case underscores the limitations of current imaging studies and emphasizes the importance of considering a wide range of potential diagnoses when dealing with pelvic masses of uncertain etiology.