This paper presents the findings of a study to investigate the value of measurements of the foramen magnum in relation to the determination of biological sex. The study performed a large-scale analysis of 250 adult individuals (male=144, female=106) from a modern Swiss population utilising CT data acquired in the context of the Virtopsy® Project. Data was analysed using discriminant function and binary logistic regression techniques and visual observations of the morphology of the foramen magnum were made to contextualise the findings. The study found that with all variables, males and females were equally classified at 66 accuracy by discriminant function analysis, where binary logistic regression was comparatively poor at classifying females despite an overall classification rate of 66.4. The morphology of the foramen magnum was classified in 88 of the sample by visual assessment according to seven shape types; however 12 of the sample was unclassified due to shape irregularities arising from asymmetry and rim complexities. This study concludes that while measurements of the foramen magnum appear to demonstrate statistically significant differences between the sexes, the ability to discriminate sex may be limited by morphological variation. This may also influence the accuracy to which sex can be determined in individual crania and thus the isolated use of this method is not advisable unless as a suggestive finding when other features of assessment are absent or limited. © 2013 Elsevier Ltd.