The shape of the dental arcade was measured in a cross-sectional study of 2,040 sets of maxillary and mandibular study casts of Caucasoids, Mongoloids, and Negroids between 4 and 20 years of age. Three methods of dental arcade analysis were used: dental arch area, dental arch index, and length of the arc of the dental arcade. Each of these computational techniques showed that a different growth pattern was shared by the three ethic groups, and important factor to be taken into consideration in orthodontic treatment.