IN a study of 65 cribriform plates from dried adult skulls the classical arrangement of the openings into medial, middle and lateral rows was observed in all but 2 cases. A nasal slit was present in 34 plates while in a further 16 the slit was replaced by a group of large openings. In 15 (23%) of the plates there was no nasal slit or analogous feature for the transmission of the anterior ethmoidal nerve. Bony defects establishing communication with the ethmoidal air cells were present in 9 plates. The microscopic appearance of these defects is consistent with their production by a process of “focal atrophy”. The dimensions of these abnormal openings, of the nasal slits and of the openings in the medial row of the plate are sufficiently large for them to be the site of leakage in non-traumatic cerebrospinal fluid rhinorrhoea.