An in vitro study was performed to determine the number and the type of root canals, their ramifications, transverse anastomoses, apical foramina locations, and frequency of apical deltas in a Turkish population. One thousand four hundred human permanent teeth were injected with India ink, decalcified, and cleared after the length of each was measured. The examination of root canal systems of the teeth was based on Vertucci's classification. The findings were used to classify the teeth into four groups. Variable root canal configurations were found in the second premolar and the mesiobuccal roots of first and second molars among the maxillary teeth and in all of the mandibular teeth, except the mandibular second premolar.