The aim of endodontic therapy is the prevention or treatment of apical periodontitis. Some years ago, 2 endodontic classification systems, the Dutch Endodontic Treatment Index (DETI) and the Endodontic Treatment Classification (ETC), were introduced in the Netherlands. These systems differentiate between complicated and uncomplicated endodontic cases. Before treatment, the systems may help in assessing the difficulties and risks of performing an endodontic treatment and in deciding whether to carry out treatment or refer the patient to an endodontist. Root canal therapy may involve considerable risks. This is illustrated with three clinical cases, which show the sort of complications that may be prevented using the 2 classification systems.