Introduction: Liposarcoma is generally classified into four subtypes: a) well-differentiated liposarcoma/atypical lipomatous tumor, b) dedifferentiated liposarcoma, c) myxoid/round cell liposarcoma, and d) pleomorphic liposarcoma. Dedifferentiated liposarcoma is mostly seen in the region of retroperitoneum. Aim: To present a case of dedifferentiated liposarcoma in a rare site of location: the lower extremity. Case Report: A 24-year-old woman presented with a firm painful mass, 3x2 cm in diameter on the medial side of left thigh. MRI demonstrated a lesion on that location showing low signal intensity on T1-wieghted and high signal intensity on T2A-wieghted sequences. After an excisional biopsy the histopathological examination via Haematoxylin and Eosin firstly revealed the diagnosis of malign undifferentiated tumor. The results of immunohistochemical evaluations were as follows: SMA (-), HMB45 (-), S100 (+, focally), Desmin (-), Vimentin (+, focally), CD68 (+, focally), CD34 (-), LCA (-), and Inhibin (-). The final histopathological diagnosis was dedifferentiated liposarcoma. Conclusions: In English-language literature data for dedifferentiated liposarcoma of the lower extremities are very restricted. Although imaging with CT and MRI, the final and distinct diagnosis is made immunohistochemically. A clinician should be aware of the presence of a dedifferentiated liposarcoma within a mass on the lower extremities.