Study Design: This was a retrospective study. Objective: The aim of this study was to test a new surgical approach, that is, "pedicle exposure technique," for atlantoaxial instability (AAI) patients with C1 posterior arches measuring <4mm, and to determine its feasibility and clinical outcomes. Summary of Background Data: C1 posterior arch screw placement is one of the most effective methods for AAI; however, several studies showed this method to be restricted when the posterior arch measures <4mm. Hence, modification of this technique is necessary to expand its indications. Patients and Methods: The average height of the C1 posterior arch in 79 AAI cases was 3.3 (range, 2.5-3.9) mm. All patients were treated by the C1 "pedicle exposure technique" and C2 pedicle screw fixation. The feasibility and clinical outcome of this technique were analyzed by postoperative x-rays, computed tomography, and Visual Analogue Score and Japan Department of Orthopedics Association score. Results: A total of 158 screws were successfully placed into the atlas in all 79 patients. There were no vertebral artery or spinal cord injuries. Venous plexus bleeding was encountered in 3 patients; there were no cases of new onset occipital neuralgia. Three screws penetrated into the external wall of the C1 lateral mass and 4 screws into the internal wall. Seventy-nine patients were followed up for 6-80 months. Bony fusion was confirmed in all cases within 3-6 months by computed tomography; there were no instrument failures. Significant differences in preoperative and postoperative Visual Analogue Score and Japan Department of Orthopedics Association score were found. Thirty-six and 15 of 62 patients with preoperative neck pain had alleviation or resolution of symptoms, respectively; 33 of 36 patients with myelopathy demonstrated significant improvement. Conclusions: The "pedicle exposure technique" is an effective alternative in patients with the C1 posterior arch measuring <4mm. In consideration of a high screw entry point on the C1 posterior arch, similar to the C1 posterior arch screw technique, we propose that this new technique can reduce venous plexus and C2 nerve root injury while providing effective biomechanical stability.