There have been several in-depth studies showing that the sternal extremity of the fourth rib can be used in estimating age as well as in determining sex, as illustrated in North American whites and blacks. Yet biological differences between populations may preclude the cross-application of standards. To test this hypothesis and develop a sex determination standard for the Turkish population, a sample of the sternal ends of the fourth rib was collected from 294 individuals autopsied in Istanbul, Turkey. Dimensions from the superior edge to the inferior one (SI) and the anterior edge to its posterior edge (AP) were measured with a caliper. The sample was divided into three age groups, "young," "old," and "total." Using discriminant function analysis, three formulae were developed, one for each group. The results indicated that SI height is the most dimorphic dimension and that both dimensions together can give an accuracy of 86% to 90%. To reach such an accuracy, the age of the unknown should be estimated, at least whether it is phase 4 or above or below, using the age standards for ribs developed by Iscan and associates. When cross-validation tests are carried out, incorrect formulae reduce accuracy by as much as 20%. Furthermore, it was observed that North American based white sex determination formulae assign many Turkish males into a female category. In conclusion, it is important to note that population and age specificity are essential in determining sex from the rib. Yet its accuracy is as good as, if not better than, many bones of the postcranial skeleton.