Sleep Apnea is a medical condition, frequently undiagnosed, that leads to significant morbidity and reduced quality of life. Patients with obstructive sleep apnea (OSA) are particularly vulnerable of developing postoperative complications when having surgery or other invasive interventions under general anesthesia; pulmonary and cardiac disorders increase the risk of perioperative complications. We propose in this article to present the importance of polysomnography in the preoperative diagnosis of patients with OSA, initiations of CPAP therapy, treatment of associated disorders for reducing peri-operatory risk of these patients.