Herein, we report a patient treated preoperatively with multiple psychiatric medications who developed serotonin syndrome (SS) during the perioperative period. SS was diagnosed using the Hunter Criteria (use of multiple serotonergic drugs preoperatively, hypertonia, and spontaneous clonus) and was presumed to have been triggered by the combination of perioperative and intraoperative serotonergic medications. It is essential that perioperative physicians, especially anesthesiologists, understand the risk factors, clinical scenario, and treatment of SS.