Ovary is the most common location of external endometrioma. It is the extension of endometriosis often misunderstood or undiagnosed. It is a source of infertility. Endometrioma, when its size is ≥ 5 cm, can be complicated by a torsion of the ovary involved. In this case it is a diagnostic and therapeutic emergency with respect to the many complications of ovarian torsion including necrosis. We report a case of endometrioma diagnosed by a torsion of the ovary. The clinical symptomatology was that of a surgical abdomen. Abdominal ultrasound was of great help for the diagnosis. But the certainty of the endometrioma was provided by the histology of the surgical specimen. The “gold standard” of management remains laparoscopic cystectomy. This indication depends on many parameters, the most important of which is the intraoperative viability of the ovary after its detorsion. Ovarian conservation improves postoperative pregnancy rates. In all cases, a GnRH analogue must be started with postoperative treatment