INTRODUCTION: IgG4-related disease (IgG4-RD) is a chronic, immune-mediated disorder characterized by widespread inflammation and fibrosis, leading to potential organ dysfunction if untreated. Often underdiagnosed due to subtle and varied symptoms, the disease can affect multiple organ systems. This case series highlights two patients who were diagnosed as cases of IgG4-related retroperitoneal fibrosis. METHODS: A total of two patients were included in this prospective case series who presented to the gastroenterology department of a tertiary care hospital with the same signs and symptoms and were diagnosed with IgG4-related retroperitoneal fibrosis (IgG4-RPF). CASE SUMMARY: Two patients were included in our case series, aged 25 and 26 years. The chief complaints included dull, radiating epigastric pain, other symptoms include diffuse abdominal pain, intensified, accompanied by nausea, vomiting, and episodic diarrhea, and a history of B-cell lymphoproliferative disorder. Endoscopic ultrasound (EUS)-)-guided biopsies were performed, showing findings consistent with (IgG4-RPF). Both patients were started on a regimen of prednisolone, pantoprazole, and vitamin D, which they tolerated well without adverse effects. They were advised to follow up with a CT scan after one month. CONCLUSION: IgG4-related disease (IgG4-RD) is a rare, chronic condition often presenting as retroperitoneal fibrosis (RPF) and affecting multiple organs. Serum IgG4 levels can be normal in certain cases, histopathological and radiological investigations are necessary for the correct diagnosis. Early initiation of immunosuppressive drugs are necessary for the disease control.