Arachnoid cysts, fluid-filled benign cysts between the dura and the brain substance, are rare developmental anomalies of the central nervous system. Although ultrasonography is used mostly in the diagnosis of arachnoid cysts, there is a paucity of information related to the fetal magnetic resonance imaging assessment of arachnoid cysts in prenatal period. Magnetic resonance imaging might be a useful imaging modality in diagnosis as well as in the assessment of concomitant other abnormalities in the antenatal period. We presented four cases of arachnoid cysts which were assessed by magnetic resonance imaging in the prenatal period.