Pelvic morphology varies between quadrupedal and bipedal primates due to locomotor behavior. Flat, posteriorly oriented ilial blades and narrow bi-acetabular distances characterize terrerstrial quadrupeds, while bipeds have curved blades with wider acetabular distance. While both groups exhibit an orthograde body plan, an ancestal characteristic for arboreality, humans as bipeds have modified this for a terrestrial environment. Due to the constraints of parturition, human females have been shown to have wider bi-acetabular distances than males, but whether or not their interspinous distance or bi-iliac breadth is different remains to be determined. The main objective of this study was to evaluate bi-iliac, interspinous, and bi-acetabular breadth in human males and females, using macaques, as the quadrupedal comparison group. Using Osirix imaging software, these pelvic dimensions were measured from the radiographs of 10 human males and females, and 11 adult macaques. Since macaques only show sexual size dimorphism in the pelvis, we did not distinguish between sexes. From the average dimensions, three ratios were calculated (bi-iliac breadth/interspinous distance (BI/IS), bi-iliac breadth/bi-acetabular distance (BI/BA), interspinous distance/bi-acetabular distance (IS/BA)). Sex and species differences were examined statistically using Stata (StataCorp, College Station, Texas). As expected, the ratios in macaques were significantly different than humans (all p’s < 0.001). While human bi-iliac breadth and interspinous distance was greater than bi-acetabular distance (all p’s < 0.001), macaques showed nearly identical proportions in the three measurements. These findings reflect different locomotor patterns morphologically shown by the transition between vertically oriented iliac blades to more anteriorly wrapped iliac blades. Between males and females, females differed from men in bi-iliac/interspinous ratio (p = 0.038). Unexpectedly, the sexes did not differ in the other two ratios. Like macaques, humans did not show evident sexual dimorphism in relative pelvic proportions.