Smooth muscle sarcoma is cancer and is a type of malignancy. Smooth muscle sarcomas are malignant tumours that originate from smooth muscle cells or from mesenchymal cells that have differentiated into smooth muscle cells, and are diverse, with symptoms varying depending on the site. The most common site is the retroperitoneal region, which accounts for approximately 50% of cases. Symptoms include abdominal masses, pain, weight loss, nausea or vomiting. Non-retroperitoneal smooth muscle sarcoma is most commonly found in the lower limbs, but can also be seen in other areas and often presents as a progressively larger, painless mass. The diagnosis of smooth muscle sarcoma requires a combination of imaging and pathological diagnosis, and prompt medical attention should be sought.