From the study of four personal cases of microgyria related to fetal CMV infection and a review of the literature it is concluded that: 1) Microgyria is a frequent neuropathological finding in this disease - 2) CMV microgyria is the result of an insufficiency of cerebral blood supply and is not due to a disturbance of neurogenesis or histogenesis as a consequence of a direct cytopathic effect of the virus on germinal cells. The way by which the CMV causes cerebral ischemia - angeitis or more probably, transient systemic perfusion failure, - is discussed, but remains obscure. Other viruses may act on the fetal brain by way of circulatory disturbances.