Many studies have shown that the oral mucosa and salivary glands are sensitive to estrogen action. However, the expression of estrogen receptors (ERs) within these tissues is an area of controversy. ERs exist as two subtypes (ER and ER ), and we hypothesized that the incongruity between ER expression and estrogen sensitivity may result from differential expression of ER subtypes in oral tissues. To test this hypothesis, we analyzed oral mucosal and salivary gland samples for ER and ER protein expression by immunohistochemistry from a cross-section of patients attending hospital for surgical problems of the head and neck. ER was not detected in oral buccal and gingival epithelium or in salivary glands. In contrast, ER was widely expressed at high levels in all oral tissues studied. Within these tissues, ER was observed primarily in keratinocytes and salivary gland acinar and ductal cells. Our results demonstrating the expression of only the ER subtype within oral tissues may explain the contradictory results from previous studies investigating ER expression in these tissues. Importantly, these results suggest that estrogens may act via ER in oral tissues and explain the effect of hormonal changes on the oral mucosa as well as on saliva secretion and composition.