For many years, a variety of abnormal endometrial lesions have been linked to endometrial cancer but have been designated as hyperplasia and classified by modifying adjectives such as cystic, adenomatous, atypical, moderate, and severe. Though descriptively distinctive, there are enough consistent histologic transitions between them to designate the entire group as belonging to a continuous spectrum from benign to malignant. Furthermore, because these epithelial lesions demonstrate not just hyperplasia but significant disorderly growth patterns, it has been suggested that they be referred to as dysplasias. In order to evaluate the association of these types of dysplasia to cancer, two groups of patients were studied. In one group, the histologic states of the endometrium of patients with endometrial cancer were retrospectively analyzed. In the second group of patients, who were selected for study because the endometria were diagnosed as belonging to the dysplastic groups, the subsequent endometrial histology was prospectively studied. The findings suggest that there is a recognizable group of endometrial lesions with an association to endometrial cancer strong enought to label and treat them as neoplastic.