Background: To evaluate the reliability of a new instrument to clinically measure the anteroposterior relationship of the maxillary central incisors to the forehead. Methods: An analytical cross-sectional study using a sample of 84 (67% female and 33% male) young adult participants was conducted. Measurements were performed according to Element II of the Andrews’ Six Elements of Orofacial Harmony by assessing the horizontal distance between the facial axis point of the maxillary central incisor and the forehead's anterior limit line. The instrument tested was a transparent plastic template having a leveling meter, reference lines, and an embedded millimeter ruler. Two orthodontists evaluated the sample twice with a minimum of a two-week interval between evaluations. The reliability was evaluated using the intraclass correlation coefficient. Repeated-measures ANOVA was also performed. Results: Good to excellent intra- and interexaminer agreement, with intraclass correlation coefficient values of 0.874 (95% confidence interval 0.800–0.921; P < 0.001) and 0.876 (95% confidence interval 0.739–0.948; P < 0.001), respectively, were calculated. There were no statistically significant differences between all the repeated measurements assessed (P = 0.820). Conclusions: The instrument showed good to excellent reliability for determining the anteroposterior relationship of the maxillary central incisors to the forehead and could be used to help orthodontists and maxillofacial surgeons indirectly evaluate the anteroposterior position of the maxilla.