Endometrial stromal sarcoma (ESS) is a malignant uterine mesenchymal tumour, which belongs to the group of endometrial stromal tumours, because of its histologic resemblance to the endometrial stroma of the functioning endometrium. ESSs are the second most common uterine sarcomas, accounting for 15–20% of them and they are divided into low-grade ESS (LG-ESS) and high-grade ESS (HG-ESS). These two entities are distinct from a histological, immunohistochemical and prognostic perspective, highlighting the crucial role of a specialised surgical pathologist. Surgery remains the cornerstone of treatment in the early stage, with, depending on the histological type, the possibility of preserving the adnexa. Adjuvant hormonal treatment can be considered in stage I LG-ESS, especially in cases of tumour morcellation. In stage I HG-ESS observation after complete resection is usually recommended. Adjuvant chemotherapy could be proposed in selected stage I patients with good performance status and with risk factors (large tumours, surgical morcellation, high mitotic index). Belonging to the wide group of soft tissue sarcomas, patients with ESS should be treated in specialised centres to give the patients the best prognosis.