Dermoid cyst is the most frequent benign ovarian tumor. Its intraperitoneal rupture may lead to a peritoneal reaction known as chemical peritonitis. It is a rare but a potentially dangerous issue. Its treatment may need one or more reoperations. We report here the case of a patient operated on in emergency for a torsion of an ovarian dermoid cyst, with peritoneal spillage of its content during coeliosurgery. The prolonged contact between the sebaceous material and the peritoneum has led to a chemical peritonitis. Two more laparoscopic interventions, associated with a systemic anti-inflammatory treatment, were necessary to relieve symptoms. We propose the following attitude to avoid this complication: (1) puncture and drainage of the cyst with a trocar; (2) extraction of the cyst in an endobag, and (3) abundant washout of the peritoneal cavity.