THE subject of endothelioma, a term first advanced by Golgi, in 1869, in describing a calcified neoplasm of the dura mater, an endothelial psammoma, forms one of the most notable topics in pathology. No chapter is more incomplete. With our meager conception of the reticulo-endothelial system, and the group of composite tissues which it composes, it is not surprising that this field should offer fertile soil for forensic deliberation among pathologists. Research, directed toward studying the histogenetic origins and capacities for variable differentiation characterizing the least understood of cell groups, would accomplish much toward settling the questions at issue. Endothelioma of the meninges, pleura, and peritoneum is characteristic, and has been accepted as authentic. Marckwald's (1) case of multiple endotheliomas of the bones is recognized by Ewing. Solitary diffuse endothelioma of the bone, or Ewing's sarcoma, is a definite entity. Multiple and single endotheliomas of the lymph nodes have been described and reported. Recklinghausen in 1897, first recognized primary endothelioma of the lymph nodes as a distinct tumor. Ewing (10) became enthusiastic in the study of these tumors, reported a number of cases, and published a monograph on the subject in 1913. However, his recent studies would show that it is still a medical curiosity. Only a few cases have been recorded in the last two decades. Its incidence varies in different medical centers, which factor is governed by the diversity of opinion as regards the true nature of endothelioma, and the hesitation of some pathologists to make this diagnosis. If the neoplastic nodes are cervical in distribution, and the type of growth is alveolar, primary carcinoma of the nasopharynx, base of the tongue, that of branchiogenic origin, as well as bronchogenic carcinoma of the superior pulmonary sulcus, must be eliminated before concluding that the lesion is one of primary endothelioma and not metastatic cryptogenic carcinoma. McNamara (22) has recently reported five cases of the multiple type. In this article, McCartney's (14) and Zaffagnini's (15) cases with positive Wassermann are mentioned. This association of syphilis with endothelioma would recall Ewing's (10) contention that the disease is often excited by chronic granulomatous infections. While endotheliomas of the uterus, ovary, and stomach have been described, they have not been accepted as typifying the classical structure of this mesenchymal tumor. No phase of the subject has suffered as much controversial discussion as that of endothelioma of the skin. Billroth first reported multiple primary malignancies seventy-five years ago, and they have long since ceased to be regarded as pathologic curiosities.