One hundred fifty-seven consecutive patients with clinical stage I endometrial adenocarcinoma who underwent primary surgical therapy between July 1979 and January 1986 were evaluated prospectively for malignant peritoneal cytology. No treatment was directed specifically for positive peritoneal cytology. Thirty patients (19%) had malignant peritoneal cytology. In univariate statistical analysis, positive cytology was significantly associated with depth of myometrial invasion (P = .02) and histopathology (P less than .025), but not with disease recurrence (P = .33). Recurrence developed in five (17%) of 30 patients with positive cytology and 11 (9%) of 127 patients with negative cytology. Using multivariate analysis, the presence of extrauterine disease spread other than lymph node metastasis was the only variable significantly associated with time to recurrence (P = .009). When patients with poor prognostic factors (grade 3 tumors, deep myometrial invasion, tumors larger than 2 cm, positive lymph nodes, and other extrauterine disease spread) were excluded from analysis, malignant peritoneal cytology still had no influence on time to recurrence. Of the five patients with positive peritoneal cytology who had disease recurrence, only one recurrence arose within the peritoneal cavity. The presence of positive peritoneal cytology in clinical stage I endometrial adenocarcinoma does not appear to have independent prognostic significance and probably should not influence treatment decisions in the absence of other poor prognostic factors.