The majority of C.S.F. fistulae are of traumatic origin and in order to avoid the threat of meningitis, they require operative closure. For the demonstration of the fronto-basal defects, multi-dimensional tomograms in various planes have proved very valuable. In 28 patients examined in the Radiological University Clinic (Münster), defects were most common in the cribriform plate. In addition to a break in its contour, one can find displacement of fragments, step formation, opacification of the adjacent nose or sinuses or intracranial air. 88% of defects could be localised in this way. The tomograms were not helpful in two very small fronto-basal fractures.