Ultrasonography has been used in neurosurgical operative procedures for several decades. The authors report the case of a large pituitary tumor that was subtotally resected using endoscopy via the transnasal-transsphenoidal approach, with the aid of transcranial real-time ultrasound. To our knowledge, this is the first reported case in which intraoperative transcranial-transdural real-time ultrasound was used to facilitate the resection of a skull base tumor.