Fifteen cases of brain tumors of supratentorial location were studied by RI cisternography; Cisternographical patterns of decreased or absent radioactivity were classified into five groups as follows: Pattern I: Sharply circumscribed and localized decrease in radioactivity; Pattern II:Ill-defined and focal decrease in radioactivity; Pattern III: Areal decrease in radioactivity involving one whole or two lobes; Pattern IV: Hemispherical decrease in radioactivity and Pattern V: Total decrease in radioactivity in the head. Each pattern appears to correspond well with topographical features of brain tumors and their related pathology, such as extracerebral tumors (pattern I), intracerebral but superficially located tumors (pattern II), extracerebral tumors with surrounding edema or large intracerebral tumors (pattern III), extracerebral or intracerebral tumors with increased intracranial pressure (pattern IV), and extremely increased intracranial pressure regardless the site of tumor (pattern V). In consideration of these patterns, RI cisternography would be a more useful supplementary method in diagnosis of brain tumors to detect the area involved, to differentiate an intracerebral from an extracerebral tumor, and to find a recurrence of the tumormfurthermore, it is helpful to know the therapeutical effects of surgery and radiotherapy. RI cisternography is a simple, relatively noninvasive method which can be used more widely.