From routine sign-out of endometrial biopsy specimens, a group of 15 endometria were identified that have a characteristic histologic pattern of inflammation that is not included in present classifications of endometritis. All but one of the women were premenopausal, and all presented with abnormal vaginal bleeding. The lesion is characterized by a patchy, focal inflammation, usually composed of lymphocytes with a variable number of neutrophils and rare macrophages centered around endometrial glands and extending into the glandular lumen with disruption and partial or subtotal necrosis of the endometrial glandular epithelium. These foci were widely dispersed, never confluent, and could be overlooked easily. Plasma cells were not found in any of the endometrial specimens despite methyl green pyronine staining of the samples. Based on the histologic characteristics of this process we have designated it focal necrotizing endometritis. The clinical significance, if any, of focal necrotizing endometritis is currently unknown.