Aim:Chiari malformations are defined as a spectrum of abnormalities of the posterior brain, including the cerebellum, brainstem, skull base, and cervical cord. Although many theories have tried to explain the etiology of Chiari malformation, its cause is still unknown. This study aimed to examine foramen magnum morphometry and shape of Chiari malformation in comparison with a control group and to contribute to the literature on whether Chiari malformation affects foramen magnum morphometry.Material and Methods:In this study, cranial magnetic resonance images of 71 people with Chiari malformation and 61 people as controls were examined. The anteroposterior diameter, transverse diameter, and area of the foramen magnum were measured, and the shape of the foramen magnum was determined.Results:In the Chiari malformation group, the anteroposterior diameter of the foramen magnum was 39.11 ± 4.29 mm, the transverse diameter was 34.25 ± 3.27 mm, and its area was 969.21 ± 199.57 mm2. These results were statistically higher in female patients in the Chiari malformation group than in the control group. No significant difference was found between male patients in the Chiari malformation group and those in the control group. Round-shaped foramen magnum was predominant in both groups, but this was not statistically significant.Conclusion:In Chiari malformation, the foramen magnum is affected. This effect can be a factor that influences development of a malformation. As a result of a malformation, the foramen magnum may have expanded due to the pressure effect. More detailed and extensive research is needed to explain this phenomenon.