Background: Angiomyolipoma (AML) is a benign mesenchymal neoplasm belonging to the family of perivascular epithelioid cell tumors (PEComas). While most AMLs arise in the kidney, extra-renal occurrences are exceptionally rare. Fat-poor variants may pose significant diagnostic challenges because of their resemblance to malignant mesenchymal neoplasms. Case Presentation: We report the case of a 58-year-old woman presenting with progressive abdominal enlargement. Imaging revealed a giant retroperitoneal mass measuring approximately 40 cm, radiologically suggestive of sarcoma. Preoperative biopsies yielded discordant diagnoses, including dedifferentiated liposarcoma and spindle-cell neoplasm with smooth muscle differentiation. Complete surgical excision was performed. Histological examination demonstrated a predominantly smooth muscle proliferation lacking atypia, necrosis, or increased mitotic activity. Extensive sampling identified focal mature adipose tissue and dysmorphic blood vessels. Immunohistochemistry showed positivity for smooth muscle actin, desmin, HMB-45, and Melan-A, confirming the diagnosis of fat-poor extra-renal retroperitoneal angiomyolipoma. Conclusion: Extra-renal angiomyolipoma is an uncommon benign neoplasm that may mimic retroperitoneal sarcoma clinically, radiologically, and histologically. Adequate sampling and appropriate immunohistochemical investigations are essential for accurate diagnosis and prevention of overtreatment.