Mongols have been shown to have a disproportionate increase in the basal angle relative to their cranial capacity. The measurement of Boogard's basal angle may therefore be used as a confirmatory sign in the radiological diagnosis of mongolism. Increase in the basal angle in a group of non-mongols with hydrocephalus and a cranial capacity above the 95th percentile has been shown to relate to the increase in capacity. The shape of the skull in mongolism is more variable than previous authors have suggested and a re-classification of cranial form in both normality and mongolism is submitted to the literature.