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The cranial base midsaggital aspect was analyzed longitudinally in 16 male and 16 female Macaca nemestrina using standardized cephalometric radiographs. Because the cranial base angle includes the superiorly-directed growth of the frontal bone, a procedure which minimizes the influence of the frontal aspect was required. Using Fourier analysis, differences in size were controlled to facilitate an analysis of changes in shape. Three areas were measured, the anterior cranial base, hypophyseal fossa and the dorsal clivus. All three showed alterations in shape with age. A maximum percent shape change was computed at 3.5 years for females and 4.5 years for males. These ages coincide with the estimated age for the pubertal spurt. Further analysis of the data showed a maximum shape difference in sexual dimorphism at 4.5 years which is also associated with the timing of the pubertal spurt.