T The extraction-non extraction debate is one of the earliest and most lasting philosopic controversies of dental practice. In Orthodontic treatment, premolar is the tooth sacrificed in most extraction cases, but almost every tooth has been considered for extraction. The subject of second molar extraction has provoked some lively debate in recent years. Second Molar extraction can relieves crowding in the posterior part of the arch and it decreases the number of third molar impaction. It can be used to advantage where third molars are present, normal in size and shape, fairly upright, the crown partially or fully formed, and the cusps clearly identified The purpose of this study is to present timing, indications, contraindications, advantage and disadvantage of second permanent molars extraction.