The clinicopathologic features of uterine serous carcinoma (USC) lacking myometrial invasion, including its putative precursor lesion endometrial intraepithelial carcinoma (EIC), have not been studied extensively. Some USCs may prove fatal even when myometrial invasion is apparently absent, whereas others may be cured with surgery alone. Accordingly, the authors studied eight cases of pure EIC (no invasion identified) and 13 superficial serous carcinomas (SSCs) in which invasion was limited to the endometrial stroma to clarify the behavior of these lesions. The review demonstrated that the most important feature in assessing prognosis is the presence or absence of extrauterine disease at presentation. Thirteen of 14 patients (93%) with EIC or SSC confined to the uterus (stage I or IIA) were disease free and one was dead of unrelated causes at 52 months, whereas seven women who presented with extrauterine disease, even if only microscopic, were either dead of disease or alive with recurrences. Accordingly, patients with EIC or SSC must undergo meticulous surgical staging at the time of hysterectomy. Because the distinction between EIC and SSC based on the identification of stromal invasion is difficult and these lesions share a unique pattern of clinical behavior, the authors regard EIC and SSC measuring 1 cm or less as "minimal uterine serous carcinoma."