The purpose of this study was to observe the changes of the lower 3rd molars following the extraction of the lower 2nd molars by Lateral Cephalograms and Orthopantomograms. The subjects consisted of twenty malocclusion, 7 males 13 females, were 19 year 5 month old at the removal of the lower 2nd molars, 19 year 1 month old at the end of the orthodontic supervision after the removal of the lower 2nd molars (mean age). The obtained results were as follows, 1. It is recommended to extract the lower 2nd molars when the lower 3rd molars are Nolla´s Stage 4 or 5. 2. With the pre-extraction variables obtained by factor analysis, it was possible to predict the long axis of the lower 3rd molars after 2nd molar extraction. 3. There were no impacted 3rd molars.