Four cases of ventricular diverticulum are presented, 2 with spontaneous ventriculostomy. In 2 patients, the cause was monoventricular hydrocephalus through congenital stenosis of the foramen of Monro, with paraventricular diverticula and spontaneous ventriculostomy. Both patients had a cystic space in the quadrigeminal and supracerebellar cistern. In one patient during pneumoencephalography, the ventricular diverticulum filled via the ventriculostomy. The other 2 patients had congenital stenosis of the Sylvian aqueduct with the formation of a large supratentoria cyst connecting with the posterior part of the third ventricule.