Leiomyosarcoma is a type of soft tissue sarcoma and one of the most common subtypes among all sarcomas. It is also the most common malignancy affecting the vascular system with an overall poor prognosis with 10-years survival rate of <60%. Leiomyosarcoma can occur with identifiable risk factors such as radiotherapy exposure or due to unidentifiable factors and genetic factors.We present a 49-year-old female patient with painful left inner thigh lump for six months which has been increasing in size. The swelling location was in the medial side of the left thigh, non-pulsatile and tender with no signs of hotness, discoloration or discharge. Ultrasound was performed and reported a subcutaneous hypoechoic well-defined lesion that is in close proximity to Great Saphenous Vein. The diagnosis was confirmed after surgical excision and was followed up by computed tomography for metastatic lesions.Cases of leiomyosarcoma is rare and usually present with painful swelling. However, non-painful and non-tender lesions can present, and clinicians should be wary of such swelling, especially when they are in close proximity to vascular area. Great saphenous vein leiomyosarcoma is difficult to diagnose solely by radiology, but ultrasound can help guide the course. Other associated factors such as deep venous thrombosis may arise.In conclusion, a thorough radiological assessment is necessary in lesions close to vascular lesions to accurately diagnose it.