Background: Subcortical nodular heterotopia is a neuronal migration disorder of uncertain etiology. This disorder occurs primarily in females and has a familial X-linked dominant inheritance pattern. The predominant symptom associated with heterotopia is seizures. Case: At 23 weeks’ gestation, prenatal sonography disclosed an isoechoic supratentorial intracranial mass causing right-sided shift of midline structures and compression of the contralateral cerebral ventricle. Serial ultrasound examinations of this mass were significant for the absence of invasion into surrounding structures, gross enlargement of cranial biometric parameters, and hydrocephalus and hydrops fetalis. Neonatal magnetic resonance imaging findings were consistent with gray matter heterotopia and were confirmed as such by brain biopsy. Conclusion: Subcortical nodular heterotopia manifested unique prenatal sonographic findings. This case suggests the possibility of prenatal diagnosis in families at risk for this lesion.