We have recently demonstrated that 16-slice multidetector CT (MDCT) is insufficient for cervical spine (CS) clearance in patients with unreliable examinations after blunt trauma. The purpose of this study was to determine if a negative CS CT using 40-slice MDCT is sufficient for ruling out CS injury in unreliable blunt trauma patients or if MRI remains necessary for definitive clearance. In addition, we sought to elucidate the frequency by which MRI alters treatment in patients with a negative CS CT who have a reliable examination with persistent clinical symptoms. The trauma registry was used to identify all patients with blunt trauma who had a negative CS CTon admission using 40-slice MDCT and a subsequent CS MRI during their hospitalization from July 2006 to July 2007. Two hundred thirteen patients were identified. Overall, 24.4 per cent patients had abnormal MRIs. Fifteen required operative repair; 23 required extended cervical collar; and 14 had collars removed. A total of 8.3 per cent of patients with an unreliable examination and 25.6 per cent of reliable patients had management changed based on MRI findings. Overall, MRI changed clinical practice in 17.8 per cent of all patients. Despite newer 40-slice CT technology, MRI continues to be necessary for CS clearance in patients with unreliable examinations or persistent symptoms.