The authors review 71 patients with triventricular hydrocephalus in whom a contrast-enhanced CT scan did not show any tumoral or vascular lesion that could have caused the hydrocephalus. The patients were subdivided into three age groups. The results of the neuroradiological examination, the surgical treatment, and the complications of the shunt procedure are analyzed, with special reference to the high number (13) of periaqueductal alterations of signal pattern found on MRI (interpreted as a "slow growing" neoplasm) and to the incidence and causes of shunt malfunction.