A case of pituitary apoplexy following the performance of a pneumoencephalogram is reported. No such a case has beem published in the literature, to the author's knowledge. The etiopathogenetic mechanism is discussed and a recomendation is made that surgery should be performed straight after completion of the pneumoencephalogram, should it show a significant supra-selar extension of a pituitary adenoma, even in the absence of increased intracranial pressure.