The influence of mental distress in generating cancer of the breasts and uterus of women has long been notorious. The testimony of Dr. Walshe (“On Cancer,” 1846, p. 155), and of Sir James Paget (“Surgical Pathology,” 3rd edition, p. 800) is sufficiently emphatic; and in my own writings I have had occasion to lay great stress upon the significance of such conditions as antecedents to malignant disease of almost every pathological variety. Among Cancer Hospital in-patients, of both sexes, symptoms of mental unsoundness are far from infrequent. It occurred to me, therefore, that an inquiry as to the actual prevalence of cancerous maladies among the insane might prove of some value, especially as such developments are becoming so increasingly frequent among us, and as anything bearing upon their peculiarities of selection or of distribution cannot well be devoid of interest to the pathological inquirer. I accordingly instituted on my own account a miniature “collective investigation,” the net results of which I now venture to lay before you, with the expression of my great indebtedness to those medical gentlemen practising in this particular field who have so kindly assisted me by courteous, and often very full, replies to my questions.