IntroductionALTHOUGH the majority of patients who sustain a closed head injury appear to make a complete and satisfactory recovery, some are left with residual disabilities, which interfere with their well-being and their adjustment to society. It is known that in such cases permanent structural changes often occur in the brain, but clinically it is difficult to ascertain their severity and extent. There is no single method of investigation which affords this information. Such methods as neurological examination, radiological investigation of the skull, psychological tests, and electro-encephalography, each contribute something to the analysis, but each has its limitations. The following study was undertaken in order to evaluate air encephalography, not so much as a method of demonstrating the presence of posttraumatic space-occupying lesions, but of assessing the degree of damage which has occurred in the brain.That changes in the outline of the ventricles often follow closed head injury was clearly established in papers from Foerster's clinic at Breslau by Schwab (1926a and b) and by Bielschowsky (1928). Both authors employed encephalography with air introduced by the lumbar route and both described three groups of cases with abnormal encephalographic findings, viz. (a) cases in which the ventricles did not fill; (b) cases with enlargement and deformity