Twenty cases of infantile triventricular hydrocephalus from non-tumoural aqueductal stenosis were treated by ventriculocisternal shunt following RISA cisternography. In 11 cases RISA cisternography showed a normal pattern of CSF circulation. One patient was lost to follow-up. Two had their intrathecal shunt converted into an extrathecal one because of postoperative meningeal infection. Of the remaining 8 patients, 7 had good and 1 fair long term results. In 9 cases RISA cisternography presented an abnormal pattern without indicating a definite impairment of CSF absorption. Slow flow of the tracer leading to its complete disappearance from 36 to 48 hours and 48 to 72 hours was observed respectively in 7 and 2 patients. In both the latter as well in two of the other seven an extrathecal shunt had to be employed (44%). A retrospective analysis to assess the predictive value of CSF absorption test by RISA in the selection of this kind of intrathecal shunt is made.