Purpose: This study was conducted to evaluate the skeletal and dental effects of the Tandem appliance in three dimensions for the correction of skeletal Class III malocclusion. Materials and methods: Twenty-two female girls with skeletal Class III malocclusion due to maxillary retrognathia were selected for this study with age of 7 to 10 years. All patients received The Tandem appliance for treatment of class III malocclusion. CBCT images and digital study models were made at two stages; before and after treatment with The Tandem appliance. CBCT images and digital study models were analyzed and data were statistically analyzed. Results: The use of Tandem appliance significantly enhanced the forward growth of the maxilla without any noticeable effects on the mandible. The anterior and posterior facial height were significantly increased. There was a significant increase in the proclination of the upper incisors and retroclination of the lower incisors. In addition, there was a significant increase in the upper and lower inter-molar widths and also, in the upper inter-canine width. Conclusion: The Tandem appliance showed effective results in the treatment of skeletal Class III malocclusions with maxillary retrognathia. It had a combination of skeletal and dental effects