Fifteen hundred sixty-six patients with adenocarcinoma of the endometrioid type (AC) were studied. These accounted for 78.9% of all 1985 patients with confirmed endometrial carcinoma diagnosed in Norway in the period 1970 through 1978. Four hundred and sixty-nine patients (29.9%) had well-differentiated tumors, 677 (43.2%) were moderately and 420 (26.8%) poorly differentiated. Eighty-one percent of the patients had surgicopathologic Stage I disease, 11% Stage II, 6% Stage III, and 2% Stage IV. Mean age at diagnosis was 62.1 years (range, 36 to 91). The crude 5-year and 10-year survival rates for all patients were 74.1% and 62.2%, respectively. Five-year crude survival was 86.8% for Grade 1 and 58.3% for Grade 3 tumors. The 5-year crude survival for patients with intramucosal tumors was 88.7% as opposed to 46.9% for patients with tumors infiltrating to the serosa. Sixty-six percent of the patients with vessel invasion survived for 5 years in contrast to 88.6% for patients without vessel invasion. Histologic grade, myometrial infiltration, vessel invasion, and lymphocyte reaction surrounding the tumor were strongly interrelated. Multivariate analysis showed that the age of the patient at the time of diagnosis was the most important single prognostic factor. Disregarding age, survival in operated patients was more dependent on the depth of myometrial invasion than on grade and stage of disease.