The recent advances in neurodiagnostic procedures have changed pneumoencephalography. Now we must find the smallest lesions and demonstrate accurately their relationships to the ventricular system cisterns and surrounding structures. Complex blurring motion tomography gives this detail, but the pediatric patients are difficult to examine and immobilization during the long exposure needed for tomography frequently compromises the airway. Hypoventilation from sedation and from the radiographic positioning may lead to increased intracranial pressure. By performing pediatric pneumoencephalography under general anesthesia, with nitrous oxide as both an anesthetic agent and as the contrast material, we are able to control patient motion, preserve the child's airway, and prevent hypoventilation. The nitrous oxide, rapidly diffusible, is a good contrast agent, as large volumes can be used and the gas leaves the ventricular system quickly after the discontinuation of the anesthetic. This rapid reabsorption and elimination of the subarachnoid gas may decrease pneumoencephalographic morbidity.