During routine anatomical dissections, the presence of the accessory muscle in the anterior area of the third distal of the forearm was determined in a 59-year-old male cadaver. This accessory muscle presents an intimate relationship with the median nerve. The described variation is also useful to the hand surgeon, as the anomalous muscle is an anatomical landmark for operations at this area. This variation may be clinically important because symptoms of median nerve compression arising from similar variations are often confused with more common causes, such as radiculopathy and carpal tunnel syndrome. To our knowledge, this variation has not been cited in recent medical literature.