The metric values of the foramen magnum (FM) were studied both by dry skull measurements and tomographic measurements. Anteroposterior (AP) and transverse diameters of 88 skulls in three different groups were taken into consideration. The mean AP value for the 38 skulls of the first group (Late Byzantine Era, A.D. 13th century) was 35.6 +/- 2.3 mm, while the mean transverse value was 29.9 +/- 2.1 mm. Twenty-seven skulls of the 20th century had the mean values of 35.1 +/- 2.8 and 28.7 +/- 2.2 mm for AP and transverse measurements, respectively. The third group consisted of computed tomography (CT) measurements of 23 outpatients in the radiology department. Their mean AP value was 36.4 +/- 2.8 and the mean transverse value was 30.0 +/- 1.4 mm. When the measurements of 88 skulls of the three groups were considered together, the mean AP value was 35.6 +/- 2.7 and the transverse value was 29.5 +/- 2.1 mm. There is no significant difference between the total mean value of the present study and that of other authors. However, if the three groups are considered separately, the mean transverse value shows significant differences, especially that of the second group. Also the radiographic and tomographic measurements of other authors have higher results than the present results, perhaps due to methodologic differences.