The objective of the present study was to determine the MDR1 gene expression in endometrial cancer. Twenty-six newly diagnosed patients with endometrial carcinoma were included in this study. Patients were treated with surgery followed by adjuvant radiotherapy. Four- to six-micrometer sections of the archival paraffin-embedded blocks were cut, deparaffinized, and stained by immunohistochemical technique using P-glycoprotein dye. Endothelial cell staining was used as the positive control of the dye. Immunostaining was categorized from 0% to 100% based on the percentage of cells stained by examining 3-4 high-power fields. The mean P-glycoprotein immunoreactivity for the whole study group was 17 +/- 25% (0-90). The mean P-glycoprotein immunoreactivity was 21 +/- 26% (0-90) for the endometrioid histology and 6 +/- 13% (0-30) for the clear cell histology. P-glycoprotein immunoreactivity was not detected in a case of mucinous histologic subtype. There was a significant negative correlation between age and P-glycoprotein immunoreactivity (r = -0.530, P = 0.005). The P-glycoprotein immunoreactivity was found to be 30% positive in only one case of clear cell histologic type out of five. However, P-glycoprotein immunoreactivity was not significantly lower in clear cell histologic subtype compared with endometrioid subtype of endometrial cancer (P = 0.116). P-glycoprotein immunoreactivity was found to be 0% in grade 1 (n = 2), 22 +/- 28% in grade 2 (n = 17), and 8 +/- 14% in grade 3 (n = 7) patients (P = 0.273). Premenopausal patients were found to have a significantly higher P-glycoprotein expression (40 +/- 33)% vs. 11 +/- 20%, P = 0.04). P-glycoprotein immunoreactivity was found to be less with advanced age in endometrial carcinoma. However, premenopausal patients were found to have a significantly higher P-glycoprotein expression.