An analysis of 1,590 consecutive primary uterine neoplasms detected over a 30-year period revealed a progressive decrease in die frequency of squamous cell cancer of the uterine cervix associated with a progressive increase in the frequency of endometrial cancer. The increasing frequency of endometrial cancer was in large part due to the emergence of a neoplasm having malignant glandular and squamous components. The clinical and morphologic features of adenosquamous cancer of the endometrium are described, compared with the findings in other endometrial cancers, and correlated with the biologic nature of the neoplasm. Compared with endometrial adenocarcinoma, the adenosquamous cancers are more readily detected by cellular methods, occur at an older age, have a shorter symptomatic period, are associated with a less differentiated glandular component, are more advanced at time of detection, and have a poor 5-year survival (less than 20%).