This report gives a description of 4 male patients, two of whom are sibs, two of whom are uncle and cousin. They appear to have psychomotor retardation, spastic quadriparesis and on CT (partial) agencies of the corpus callosum, and irregular lining of the lateral ventricles, without craniofacial abnormalities or seizures. Although the mode of inheritance of agenesis of the corpus callosum is still difficult to establish, in these 4 male patients an X-linked recessive inheritance is the most likely mode. A review of the literature with concern to the heredity of agenesis of the corpus callosum is presented. The clinical and neurological findings in the present four male patients allow for the delineation of a new X-linked mental retardation syndrome.