Most tumors affecting Vater's ampulla are adenocarcinomas, and other histological variants are less frequent. Signet ring cell carcinoma is more commonly found in the stomach than at other sites of the digestive system. Signet ring cell carcinoma of the Vater's ampulla is extremely rare, and only 15 cases have previously been described in the literature. It mainly occurs in elderly patients (median age = 57 years). We report a case of advanced signet ring cell carcinoma of the ampulla of Vater, with invasion of the duodenum (D3) admitted in the Medical Oncology Unit of HASSAN II University Hospital.