The purposes of this study were to clarify the effect of tooth size and arch size upon the crowding. 175 upper casts were measured and following conclusions were made. 1. Tooth size, intermolar width, 2nd premolar width of crowded group were not significantly different from those of noncrowded groups. 2. Intercanine width, arch length of noncrowded group were significantly larger than crowded group. 3. Multiple regression equations were derived by using tooth size, arch perimeter, arch length, intermolar width.