Objective: The aim of this study was to evaluate the changes in mandibular and maxillary third molars in cases treated with and without extraction. Materials and methods: Pre-treatment (T1) and post-treatment (T2) radiographs were taken of 46 subjects who had been treated without extraction and 44 subjects who had been treated with extraction of premolars. Results: The increase of eruption space and the improvement of the angular position of third molars were statistically significant between extraction and non-extraction orthodontic treatment, whereas, there was no statistically significant difference between first premolar extraction and second premolar extraction. Conclusion: Third molar impaction for orthodontic patients can be predicted before treatment according to the size of retro molar space and the type of treatment with or without premolar extraction.