© 2020 The Society of Obstetricians and Gynaecologists of Canada/La Société des obstétriciens et gynécologues du Canada.Background: Primary retroperitoneal Müllerian adenocarcinoma (PRMA) is a very rare type of primary retroperitoneal tumour. Case 1: A 45-year-old woman presented with left lower extremity swelling and pain. Imaging revealed that the tumour had invaded the left common iliac vein and artery, internal and external iliac arteries, sciatic and obturator nerves, and pelvic wall. Case 2: A 37-year-old was admitted with pelvic pain. Imaging showed the tumor at the left iliac bifurcation infiltrating the internal iliac artery and left sciatic, obturator, and femoral nerves. Both of these patients were treated with radical surgery that achieved no visible tumour at the end of the operation. Conclusion: There is no guideline for the diagnosis and management of this entity due to its rarity. These cases should be managed at highly specialized centres with expertise in radical surgery.