Morphological traits of the posterior ilium are commonly used for sex determination in bioarcheological and forensic skeletal analysis. This study was designed to compare the classification correctness of standard scoring systems and measurements of the posterior ilium, including using logistic regression, to develop new formulae to predict sex. Metric measurements and morphological scores for the preauricular sulcus (PS), the elevation of the auricular surface, and the greater sciatic notch width were recorded for 97 males and 101 females of both European and African ancestry from the William M. Bass and Terry Collections. Correct classification of sex was high using individual traits such as the greater sciatic notch score (88.4 percent), the presence or absence of a PS (78.8 percent), and the scoring of a present PS as 1, 2, or 3 (100 percent). Furthermore, an equation combining multiple traits of the posterior ilium had a high classification of 94.9 percent. Abstract published by arrangement with John Wiley & Sons.