Three infants are reported with a recognizable pattern of defects consisting of severe microcephaly, overlapping sutures, prominence of the occipital bone, and scalp rugae. This condition, which we think represents microhydranencephaly, appears to be produced by partial brain destruction during the second or third trimester, diminution in intracranial hydrostatic pressure, and subsequent collapse of the fetal skull. Several different causes for this condition have been suggested including partial disruption of the blood supply to the brain and prenatal viral infection.