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Fifty dentate maxillary casts, obtained from thirty-four males and sixteen females, were mounted in the three-dimensional co-ordinate system of a contour meter. A transverse line of reference (x-axis) was drawn through the distal contact points of the maxillary canines, at a right angle to the y-axis which passed through the contact points of the maxillary central incisors. Relative to the canine-to-canine baseline, the locations of the lateral borders of the right and left first primary rugae were determined. The rugae were distributed on both the anterior and posterior sides of the baseline, and the anterior and posterior distances from the baseline were on the average about 1 mm. The age of the subjects, ranging from 12 to 52 years, appeared to be unrelated to the frequencies of anteriorly and posteriorly positioned rugae. Right and left first primary rugae, located on the anterior side of the baseline, showed a minute asymmetry in their topography. By contrast, there was topographical symmetry when the rugae were located on the posterior side of the baseline.