The goal of the current study was to provide an easy to use criterion to diagnose neurocranial asymmetries. An anatomical survey of the external aspect of the skull base was planned to correlate with radiological studies. In a sample of 239 skulls, variations of the angular relationship between the structures seen on a basilar view of the cranium were analysed. An anterior and a posterior transverse line were plotted with respect to the midline. Departures from 90° to the midline for either of the transverse lines were less than 5° in normal skulls, between 5° and 7° in skulls classed by independent inspection as asymmetric, and more than 7° in obviously malformed skulls.