 Despite continuing improvements in surgical procedures and ancillary care, post surgery pain continues to be a nearly universal patient experience following major operative procedures. Opioids provide considerable pain relief, but they have multiple adverse side effects and are not entirely effective. For cancer patients, uncontrolled postoperative pain can have a substantial negative effect on quality of life, can slow recovery, increase the likelihood of complications, and contribute to poorer postoperative outcomes. The identification of novel modifiable patient risk factors for post surgery pain that could become the target of presurgery interventions is thus an important goal. We will conduct a randomized, placebo-controlled, double-blind intervention trial design to evaluate the effects of an FDA approved hypnotic zolpidem on post surgery pain. Since presurgery psychological factors e.g., heightened anxiety are known to predict the severity of post surgical pain and may be associated with poor sleep, we will also assess psychological factors with questionnaires as well as sleep using actigraphy in order to determine their individual and combined impact on womens experiences of post surgery pain in this stressful clinical context. Aim 1: To determine the impact of zolpidem administered the night prior to endometrial cancer surgery on womens experiences of pain over the initial 7-10 day follow-up period after surgery using a double-blind placebo-controlled design final n128. Aim 2: To investigate psychological factors on the morning before surgery, as well as objective sleep variables on the night before surgery, as possible mediators of the beneficial effects of zolpidem on post surgery pain. Aim 3: To examine psychological factors, as well as sleep variables, assessed prior to the sleep intervention as possible moderators of the ameliorative effects of zolpidem on post surgery pain. The results of the proposed exploratory study would provide the preliminary data necessary for an R01 application to support more comprehensive investigations, including explorations of biological mechanisms underlying the preventative effects of better presurgery sleep on patients experiences of post surgery pain. 