Tissue samples of 40 patients with histologically confirmed endometrial cancer were analyzed immunohistochemically on paraffin-embedded specimens to detect ras p21 protein expression. The relationship between p21 protein expression and clinicopathological findings was also analyzed. The intensity and distribution of specific cytoplasmatic staining were evaluated semiquantitatively by counting the immunohistochemical H-score. ras p21 expression was found in 30 (75%) of 40 human endometrial carcinomas, regardless of the clinical stage of the disease. Positive immunostaining for p21 was noted in 68% of stage I-II and in all 8 of the advanced stages (III-IV according to FIGO) of endometrial carcinomas. Myometrial invasion was related to ras p21 immunostaining (p = 0.009), however, no correlation between histological findings and ras p21 expression was observed.