Prenatally diagnosed thrombosis of the torcular herophili is very rare, and it is sometimes misdisgnosed due to unfamiliarity. Sonography with color Doppler imaging is the key imaging modality for prenatal diagnosis of torcular herophili thrombosis. Typical prenatal sonographic findings include a well-defined triangular anechoic collection in the occipital region and an echogenic structure within the collection, which represents the thrombus. Fetal magnetic resonance imaging is usually used as an adjunctive modality for prenatal diagnosis, as it confirms the diagnosis by providing more precise anatomic information and better characterization of the lesion. We present 2 cases of thrombosis of an ectatic torcular herophili with serial sonographic and magnetic resonance imaging examinations, as well as a review of the literature regarding the prenatal diagnosis of torcular herophili thrombosis.