Primary soft tissue non-Hodgkin lymphoma (NHL) of the extremities is very rare. The clinical features of NHL mimic those of other soft tissue tumors, particularly sarcoma; however, they should be differentiated, as the treatment and prognosis are completely different. In this study, the case of a 68-year-old female with a giant mass, movement disorder, numbness and painful sensations in the right thigh is presented. Magnetic resonance (MR) imaging revealed a huge circle-shaped mass. Fine needle aspiration cytology (FNAC) of the tumor demonstrated neoplastic small, round cells. The tentative diagnosis was of a mesenchymal sarcoma. The right thigh was amputated. On histological examination of the amputated extremity, the diagnosis was found to be large B cell lymphoma. Primary soft tissue NHL of the extremities is a systemic malignant disease and is sensitive to chemotherapy and radiotherapy. The histological diagnosis should be identified as far as possible before the tumor is widely excised.