Twenty primary endometrial carcinomas in 40 year-old or younger women were collected from a series of 845 carcinomas and newly re-evaluated. The typical histological profile was well-differentiated adenocarcinoma (30%) or adenoacanthoma (35%); however, a case of adenosquamous carcinoma and an exceptional malignant mixed mesodermal tumor were also observed. No tendency for myometrial infiltration (M0) was displayed by 11 (55%) of the cases, while 6 were M1 and 3 were M2 infiltrating neoplasias. Adenomatous hyperplasia was associated with cancer in 53% of the 15 assessable cases. Histopathological diagnostic problems were elicited in 5 cases only. Typical Stein-Leventhal syndrome occurred in 7 patients (35%), while polycystic ovaries were observed in 15 cases (75%). Usually, the patients were obese (40%) and nulligravida (65%). All but one case were stage I disease. Prognosis seems to be excellent following surgery.