The mental foramen is an important landmark for identifying the mental nerve, and the accessory mental foramen is a rare anatomical variation. This article describes the use of computed tomo- graphy (CT) to detect an accessory mental foramen that was initially misdiagnosed as a radiolu- cent tumour in the right premolar region of a 39-year-old woman by panoramic radiography. The case suggests that preoperative CT should be performed to detect any anatomical variations. This knowledge would help in diagnosis, preoperative planning and prevention of intraoperative nerve or vascular injury.