The objective of this study was to evaluate the accuracy of frozen sections (FS) as a method for estimation of the depth of myometrial invasion in patients with stage I endometrial carcinoma. During a 3-year period (1989-1992), 46 consecutive patients with FIGO stage I endometrial carcinoma were included in this study. The depth of myometrial invasion was estimated by FS examination performed during surgery. The final histologic findings of the surgical specimen were compared to the FS evaluation. The results of this study demonstrate that deep or superficial myometrial invasions were correctly diagnosed by FS in 42 out of 46 cases (91.3%). Three cases (6.6%) with deep myometrial invasion were falsely diagnosed as superficially invasive. One case with superficial invasion (2.1%) was falsely diagnosed as deeply invasive. In conclusion, intraoperative FS examination of depth of myometrial invasion by endometrial carcinoma is a simple and accurate method, providing a good correlation with the final histologic report of the surgical specimen.