Ultrasonographic demonstration of periventricular cysts is usually associated with cystic periventricular leucomalacia due to necrosis of periventricular unmyelinated white matter. Cystic spaces with a similar appearance may also arise from prenatal lysis of fetal periventricular matrix tissue, rather than immature white matter. The resultant empty spaces are called "pseudocysts" or germinolytic cysts. Neuropathological studies have shown that germinolytic cysts may arise in Zellweger syndrome (generalized peroxisomal disorder). Here, we report their ultrasonographic demonstration in Zellweger syndrome, emphasizing the potential value of this sign in the diagnosis.