In this study two groups of dental study models were selected to evaluate the relationship between the tooth size, arch dimensions , and dental crowding. The first group consisting of 56 pairs of dental study models (28 males and 28 females) with normal occlusion ( without dental crowding) ranging in age from 16 to 20 years, were selected among 4445 students from Kerman by multi stage random sampling method. The second group consisting of 65 pairs of dental study models (12 males and 53 females) with class 1 malocclusion between the age of 16 to 26 years, were selected among the patients of three private orthodontic clinics and the orthodontic department of school of dentistry in Kerman. Mesiodistal tooth diameters, buccal and lingual dental arch widths, dental arch perimeter s and dental arch length measured in two groups. The student "t" test was used for statistical analysis of the relevant data.the tooth size in crowded group was generally larger than the noncrowded group, and the dental arch width was smaller in the crowded group. No significant differences were found in dental arch perimeters and dental arch length between the two groups. Therefore it seems that in the crowded group, dental crowding is caused by both excessively large teeth and excessively small dental arch widths especially in maxilla.