Endometrial stromal sarcoma of the uterus (ESS) is a rare lesion that can c
ause diagnostic difficulty especially when it presents with unusual histolo
gic features such as diffuse endometrioid glandular differentiation. Only t
hree such cases have been reported, all primary in the uterus. We report th
e first case of an extrauterine low-grade ESS with extensive glandular diff
erentiation that appeared to arise in endometriosis.