Experience over a period of twenty years has taught us that the occurrence of multiple primary cancer is much more frequent than we have been inclined to believe. Most pathologists are agreed that the initial lesion of cancer is generally solitary. During the past fifty years, however, they have become more cognizant of the fact that more than one primary germ center may occur in a given system or organ. Such occurrences are now recognized as primary multiplicity of malignant lesions. Many writers on the subject have called attention to the rarity of this condition, but as more data are accumulated in hospitals, especially those devoted to the study of cancer, many more instances of multiple malignancy are encountered.