Superficial leiomyosarcoma is an exceeding uncommon malignant tumor, which can be located either cutaneous or subcutaneous tissues. It may occur anywhere in the body, but there is a predilection for the thighs. The distinction between cutaneous or subcutaneous, increased mass size (> 5 cm) and depth are considered to have worst prognosis in terms of recurrence and metastasis. We report a rare case of an 81-year-old woman, presented with a 20-cm leiomyosarcoma of the shoulder. The patient reported that the mass was completely asymptomatic and its growth was slow. A CT study showed a lesion closely apposed to the head of the humerus and revealed no a clear relationship with the surrounding muscles. There was no regional lymphadenopathy or the evidence of metastatic disease. After tumor resection, a large skin and soft-tissue defect was remained and the repair was performed by myocutaneous rotational free flap of latissimus dorsi. The conclusion of the histological analysis was: subcutaneous leiomyosarcoma pT2--grade 1+ (NCI system). The delayed diagnosis and the surgical treatment and giant size of soft tissue leiomyosarcoma may adversely affect the final result.