Since the introduction of the liver treatment for pernicious anæmia some four years ago that disease has received considerable publicity. It has been generally recognized as having three main clinical manifestations. Thus it may show itself as a blood disease, as a gastro-intestinal disease, or as a nervous lesion (subacute combined degeneration of the cord). It is, however, by no means generally recognized that pernicious anæmia has yet another way of manifesting itself, viz., by the occurrence of mental disorder. The object of this paper is to emphasize this fourth aspect of pernicious anæmia. In this country the subject has not hitherto received the consideration which is due to it. Nevertheless, a number of observers in other countries have shown, both by their own personal observations and from statistics, that mental disorders are frequently met with in the course of pernicious anæmia. The degree of mental affection varies in different cases. There may be merely a modification of character, with irritability and changing mood. W. Richardson would include in this mild group many patients described as uncooperative.