The names "idiopathic" or "functional" uterine hemorrhage are generally given to a condition characterized by some form of abnormal uterine bleeding occurring in a woman in whom a pelvic examination fails to reveal any palpable lesion as the etiologic factor. It is thus not a definite clinical entity but represents a number of disturbances that manifest themselves with this outstanding symptom. The endometrium is of paramount importance in all such cases, even though the primary cause of the disease is seldom to be found in this tissue and it merely reflects an abnormality arising in the ovary or some other organ. The present study is an attempt to analyze the histologic changes in the endometrium in a series of patients presenting this condition. In all, ninety cases have been considered in which no gross changes, such as fibromyomas, malignant tumors, pelvic inflammatory disease or extensive erosions of the cervix, could