Posterior fossa malformations are among the most common brain anomalies identified by current fetal imaging techniques. The primary reason for performing fetal imaging is to gather accurate information about fetal structure on which to base reliable counseling. Despite the rapid progress in fetal imaging, the prenatal diagnosis of PF dysgenesis remains challenging due to both false-positive and false-negative diagnoses. Using ultrasonography is still the first-line diagnostic examination for fetal central nervous system anomalies. But when a questionable abnormality is visualized at US or when an abnormality is definite but the exact diagnosis is uncertain especially if suspected fetal posterior fossa anomalies, alternative imaging modality is important for decreasing ambiguity in the counseling of expectant parents. Fetal magnetic resonance imaging has become a valuable adjunct to prenatal sonography, in particular with the development of ultra-fast T2-W technique.