I. GENERAL CONSIDERATIONS Since the introduction of cerebral pneumography by Walter E. Dandy,1many works bearing on the interpretation of the pneumogram have been forthcoming.2The use of the pneumogram in diagnosis indeed made it possible to transform what would be for many patients an exploration of the brain into an exploration of the pathologic condition of the brain. The pneumograph is an instrument of precision, and as such its safety and usefulness will be proportional to specialized knowledge and experience. The day has passed for criticism of pneumography on the basis of its inherent dangers. When one compares the tragic nature of intracranial disease requiring surgical intervention with the treasured information that pneumography provides, the latter has no danger. I have adopted the policy of attempting to fill the ventricular spaces completely with air, so as to obtain as complete a ventriculogram as possible under the circumstances.