Objective : Chronic subdural hematomas (CSDH) are more common on the left hemisphere than on the right. We verified this left predilection of CSDH and tried to explain the reason for this discrepancy. Methods : We investigated the laterality of CSDH in 182 patients who were treated from January 2005 to December 2009. We examined the symmetry of the cranium and the location of the lesion. Results : CSDH was more common on the left-side. The cranium was symmetric in 63 patients, asymmetric in 119 patients. The asymmetric crania were flat on the right-side in 77 patients, on the left-side in 42 patients. The density of the CSDHs was hypodense in 29 patients, isodense 132 patients, and the others in 21 patients. Bilateral hematomas were more common in the hypodense group. In the right flat crania, the hematoma was more commonly located on the opposite side of the flat side. While in the left flat crania, the hematoma was more common on the same side. Conclusion : CSDHs occurred more frequently on the left side. The anatomical asymmetry of the cranium influences the left predilection of CSDH.