Leiomyosarcoma (LMS) represents an aggressive neoplasm that often involves a diagnostic challenge when encountered in atypical anatomical sites. The case here exposed involves a 70-year-old female with a retroperitoneal mass measuring 65mm×65mm, likely of adrenal origin, warranting consideration for adrenalectomy. Histopathological examination reveals spindle cells arranged in intersecting fascicles, displaying pleomorphism and necrosis, and is immunohistochemically positive for actin and desmin markers. The definitive diagnosis is LMS, demonstrating venous origin without infiltration of the adrenal gland. Regrettably, the patient succumbed to post-operative complications. The inconspicuous nature of LMS in this anatomical niche complicates preclinical detection, underscoring the pivotal role of histopathological analysis in its identification. Furthermore, achieving complete excision proves challenging, resulting in a poorer prognosis compared to conventional LMS, despite the availability of alternative treatment modalities. Given the absence of standardized management protocols, a multidisciplinary approach remains essential.