Endometrial endometrioid carcinoma is related to estrogen excess and expression of estrogen and progesterone receptors. Epidemiological evidence suggests that exposure to elevated androgens, as in polycystic ovarian syndrome, increases the risk of endometrial cancer. Factors impacting androgen receptor (AR) expression are not well studied. Mismatch repair (MMR) deficiency due to MLH1 gene methylation is one of the most common molecular alterations in endometrial cancer, occurring in 15% to 20% of cases. MLH1 methylation can be associated with decreased expression of other genes, so we examined the effect of MMR status on AR expression. As NF-κB is known to induce AR, this transcription factor was also examined. Three hundred forty-four unselected endometrial carcinomas were evaluated for DNA MMR. Loss of expression of MLH1 with MLH1 methylation was defined as MMR deficient, and positive expression of MMR proteins was defined as MMR intact. A case-control cohort of 96 grade 2 endometrioid carcinomas was studied from this set (47 MMR deficient, 49 MMR intact). Cases were matched for histotype, grade, and age. AR and NF-κB immunohistochemical expression were evaluated by 2 different scoring systems (CAP/ASCO and Allred) used for estrogen receptor. Despite higher levels of NF-κB, MMR deficiency was associated with a significantly lower mean percentage of AR expression. The MMR deficient group had more variable AR expression, with more cases scoring on the lower end of the spectrum. These findings have implications for clinical trials of AR antagonists in gynecologic cancers.