The report which follows constitutes the proceedings of a sym posium on the classification of brain tumours held in Cologne in 1961. It contains the contributions and discussions reported as far' as possible in a word-for-word manner, in the hope not only of providing out of the thoughts of the participants stimulation for further research, but also to indicate the atmosphere which prevailed during the symposium in which many completely opposed views were able to be expressed without any feeling of embarrassment. This freedom of expression is already obvious in the discussion of a proposed...