Eight hundred thirty-nine clinical stage I endometrial carcinoma patients diagnosed between 1979 and 1988 were treated at the University Hospital in Linköping. Forty-two (5%) had uterine papillary serous carcinoma of which 52% died of their disease. The recurrence rate, defined as new evidence of disease 6 months or more after termination of the initial treatment, was 31% among the UPSC patients compared to 6% in the non-UPSC group. The site of recurrence also differed significantly between the two groups, with the abdomen as the most common site among UPSC patients (46%) and the vagina (34%) among the ordinary adenocarcinoma patients. All UPSC patients with recurrence died of their malignancy compared to 61% of the ordinary adenocarcinoma patients. Ninety percent of isolated vaginal recurrences in ordinary adenocarcinoma patients (17) were diagnosed at a scheduled outpatient checkup. Of these, 13 are alive with no known disease after treatment.