The traditional method of classifying the causes of spontaneous abortion divides them into two major groups, fetal and maternal, each of which is again divided into numerous subgroups more or less ill defined. As a practical basis for diagnosis and treatment such an analysis tends to be confusing rather than helpful. Every accomplished abortion includes three events: death of the embryo, separation of the ovum from its attachments and expulsive uterine contractions. Any one of these may be the primary event in a given case, followed sooner or later by the other two. Thus abortion can be induced by killing the ovum with x-rays, by dislodging it with the curet or by provoking effective uterine contractions with bougies. In the same way spontaneous abortions are initiated by accidents of three general types. A consideration of the causes from this point of view clarifies certain aspects of the problem of clinical