Aim: To investigate the effect of a modified tongue crib appliance in Class II Division 1 patients with anterior tongue thrust and mandibular deficiency. Methods: Twenty-three patients (14 females, 9 males) with a mean age of 10.09 ± 1.02 years, a moderate Class II Division 1 occlusion due to a mandibular deficiency, and a mean overbite of –1.1 ± 0.8 mm were treated with a mandibular tongue crib device. Pre- and posttreatment lateral cephalograms were obtained and traced, and various angular and linear variables were measured. These measurements were compared using the paired t test. Results: The statistical assessment indicated that SNB, facial angle, B-VL, Pog-VL, and interincisal angle increased significantly. IMPA, 1-SN, ANB, and Wits appraisal were significantly decreased (P < .05). The changes of Jarabak Index, SN-MP, SNA, and Y-axis were not significant. In addition, the overjet was reduced. Conclusion: During the mixed dentition phase, a tongue crib appliance in the mandible is helpful to impede tongue thrust and stimulate mandibular growth. World J Orthod 2010;11:23–26.