Mullerian duct cysts are considered to be part of the urogenital cysts. Mullerian cysts, anatomically distant to the genitourinary organs or the pelvis, are extremely rare entities. Case report and review of the literature using key word "Mullerian cyst", "retroperitoneal" and "mediastinal". A 48-year-old woman with abdominal discomfort and nausea was referred to our hospital. Further work-up with CT and MRI showed a large retrogastric, retropancreatic cyst, herniating through the diaphragm in the mediastinum. As etiology was unsure, a laparoscopic cystectomy was performed. Histological examination showed a benign cyst of Mullerian origin. A review of the literature confirmed that extrapelvic Mullerian cysts are rare, with only 28 mediastinal cysts and 12 extrapelvic retroperitoneal cysts being described. Retroperitoneal Mullerian cysts outside the pelvis have infrequently been described in the literature. As correct preoperative diagnosis is seldom possible, surgical resection is the gold standard of treatment.