Objective: We previously reported that oral administration of the selective cyclooxygenase-2 (COX-2) inhibitor etodolac results in antitumor effects in endometrial cancer tissue. Herein, we investigated whether these antitumor effects could be assessed using endometrial cytological findings. Study Design: Etodolac (400 mg b.i.d. for 2 weeks) was administered preoperatively to 21 endometrial cancer patients: 16 had COX-2-positive disease and 5 had COX-2-negative disease. Twenty-one pairs of pre- and post-etodolac-treatment endometrial cytological samples were collected to review changes in the cytological features. Results: In the COX-2-positive patients, nuclear atypia was slightly decreased in 3 of the 16 cases, while the mitotic index was decreased in all cases. Cellular overlapping and tumor cell cluster outlines were somewhat affected in 6 and 8 cases, respectively. Nuclear/cytoplasmic ratio, anisokaryosis and hyperchromasia were also reduced in 6, 4, and 2 cases, respectively; however, tumor diathesis and nucleoli features were unchanged. In contrast, endometrial cytological features did not appear to be affected in the 5 COX-2-negative patients. Conclusions: We conclude that the antitumor effects observed in endometrial cancer tissues following oral administration of etodolac are reflected in and can be easily assessed by evaluating endometrial cytological features.