Twenty-five years of experience in the field of length measurements of the root canal are summarized. It must be concluded that there is no absolutely accurate method to measure the length of the root canal in vivo because of the specific anatomic conditions and the sources or error inherent in all methods. Of the various methods, preference should be given to the so-called graduated instruments. They do not require additional work and enable the observation of aseptic precautions. The industry must be requested to make these instruments available again.