Ankyloglossia is a congenital anomaly characterized by a short lingual frenulum and severe form needs release surgery. Our goal in this study was to confirm the long-term safety and efficacy of Z-plasty with genioglossus myotomy compared with traditional Z-plasty alone and to develop a proper measurement tool to validate the postoperative results of release operations for ankyloglossia. Patients were divided in 2 groups, release with Z-plasty only group (group 1) and Z-plasty combined with genioglossus myotomy group (group 2) In group 2, the release of central longitudinal fiber of genioglossus muscle was added in the conventional Z-plasty operative procedure. To analyze the results of the surgery, we developed an objective assessment tool which is the direct length from the innermost point of the floor of mouth to the tip of the tongue, preoperatively and postoperatively, which is called "functional tongue length." A total of 101 patients with ankyloglossia ranging in age from 36 months to 8 years underwent release operation. Although there was no significant difference in terms of postoperative measurements between groups in Kotlow class II, group 2 patients in Class III and IV showed greater postoperative functional tongue length. Also, there was no significant complication requiring secondary surgery. Our study demonstrated that adding genioglossus myotomy to a simple Z-plasty is a safe and effective method for improving the tongue mobility required to make lingual sounds, especially in moderate to severe form of ankyloglossia, along with suggestion of a new measurement tool, which can objectively assess tongue mobility with possibility for universal utilization in ankyloglossia release operation.