INTRODUCTIONDelirium is an acute and transient brain dysfunction characterized by attention disorders, disturbance of consciousness levels, and changes in cognitive function, often with noticeable fluctuations. Postoperative delirium (POD) typically occurs within 24 to 72 hours after surgery.1 The incidence of delirium after vascular surgery ranges from 5% to 39%.2 However, delirium with unilateral pupil dilation has never been reported. The appearance of pupil dilation in patients with delirium brings serious difficulties to clinical diagnosis. Here, we report an unusual case of severe delirium with unilateral reversible pupil dilation after interventional thrombectomy of the lower extremity.