Median nerve entrapment with forearm fracture is rare, and surgical exploration in the early stage is rarely performed. We report the case of a 19-year-old man presenting with severe pain and numbness of the thumb, index, and middle fingers and half of the ring finger along with weakness of abduction and opposition of the thumb after fracture of the radial shaft. These symptoms remained unimproved despite precise closed reduction and cast immobilization. The radius fracture was barely displaced, but complaints were increasing, particularly when the wrist and/or fingers were stretched. This suggested direct involvement of the median nerve at the fracture site, so magnetic resonance imaging (MRI) of the forearm was performed to identify any entrapment. Short tau inversion recovery MRI visualized significant deviation and entrapment of the median nerve at the fracture site. Surgical release of the entrapment was performed immediately, and complaints resolved shortly thereafter. A positive Tinel sign from the palm to the fingertips and recovery of abduction and opposition of the thumb were seen at 6 months postoperatively. This report highlights the utility of MRI for detecting median nerve entrapment at a fracture site, allowing immediate surgical release.