Fetal intracranial pathology detected in the early second trimester during 1237 transvaginal sonographic scans is presented. In a sharp contrast to simple choroid cysts, which disappear at the end of the second trimester as part of a benign course, gross distortion of the choroid plexus was found to be related to the later diagnosis of hydrocephalus. Three patterns of this abnormality are early absence of the plexus, hypoplasia and shrinkage, and "Swiss cheese" appearance. Ventriculomegaly in hydropic fetuses does not distort the normal architecture of the choroid plexus. Certain abnormal features of the choroid plexus, observed as early as the 14th week, menstrual age, are landmarks of developing hydrocephalus, currently detectable only later in pregnancy.