Conventional Endodontic therapy is the treatment of choice for pulp disease and periapical lesions due to pulp necrosis. Although the percentage of success of endodontic therapy is fairly high, in several cases endodontic therapy cannot perform accurately, or it is impossible to undertaken so as to avoid extraction of tooth. Before an endodontic surgery is performed a conventional endodontic therapy must be attempted because this increases prognosis and reduces the possibilities of failure. The possible presence of lateral canals, communication between periodontal ligament and infected canals through dentinal tubules and the potential hermetic reverse filling, are ones of the main factors which support the necessity of endodontic therapy. Apart from these, many cases have been reported where the basic factor of endodontic surgery failure was not the awkward operations, but the absence of the root canal filling. In this paper authors describe the basic steps and techniques which must be followed so as to avoid the failure of endodontic surgery.