A clinical, histologic and microradiographic investigation of 62 natal, neonatal and otherwise pre-erupted teeth from 51 children is presented. Such a comprehensive material has not previously been reviewed. Of the 62 teeth, 59 were mandibular incisors. A hereditary factor could be demonstrated in 12 cases. Fifty-three teeth showed more or less pronounced enamel hypoplasia. The enamel had a normal prism structure and mineralization with the exception of 22 cases where the prism structure was absent in the cervical part of the enamel. The cervical and apical dentin was atubular and in developing teeth the dentin in these regions changed to an irregularly formed hard tissue of osteodentin character, in which enclosed cells could be observed. Developing teeth often had no cementum, and in those cases where acellular cementum could be observed it was thinner than normal. In four patients atypically located carious lesions occurred.