A sibship consisting of three siblings, one male and two females with unrelated parents, showed a clinical syndrome including: infantile spasms with hypsarrhythmia, microcephaly, severe mental retardation and spastic quadriplegia. The pneumoencephalogram performed in two sibs showed agenesis of the corpus callosum and aqueductal stenosis with tri-ventricular dilatation. The disorder did not show a progressive course with deterioration of mental and neurologic functions. No biochemical or cytogenetic defect could be identified. Complement fixation for cytomegalovirus was negative. This syndrome complex is probably inherited as an autosomal recessive trait. The clinical and the genetic aspects of the syndrome are discussed.