The cemento-enamel junction (CEJ) of human teeth has been studied very infrequently and on the basis of ground sections only. A total of 30 human teeth (incisors, premolars, molars) was prepared for examination with the scanning electron microscope (SEM). A selection of freshly erupted first premolars (n=8) and third molars (n=8) served for a quantitative determination of the entire, as well as the site-specific (buccal, distal, oral and mesial aspects), length of the CEJ and of the respective extension of the 3 hard tissue relationships along the CEJ. In addition, 4 third molars were used to examine the CEJ in ground sections, using both the light- and the scanning electron microscope. In first premolars, most of the CEJ revealed edge-to-edge contact of cementum and enamel, while in 17 (maxillary premolars) to 31% (mandibular premolars) of the CEJ cementum overlapped the enamel. In third molars, cementum overlap occurred in about 50% of the CEJ, the rest showing either edge-to-edge contact of cementum and enamel or exposed dentine. In molars, the type and extension of these relationships changed from buccal-to-distal to oral-to-mesial aspects. Because of an unpredictable variation in these relationships over short distances, examination of ground sections may fail to correctly identify the CEJ-structure.