In 190 dental casts of Korean adults, 78 males and 112 females, the author measured cuspal distances beween the lingual cusps of the samed named teeth. And following conclusions were obtained : 1. In maxillary dental arch, the smallest measurement was revealed in the interpremolar distance in both sexes. 2. In mandibular dental arch, the intercanine distance was the smallest, and then measurements were increased in molar region. 3. In both sexes the intermolar distance was smaller than the central incisor to first molar distance.