OBJECTIVES: Non-adherence rates with oral endocrine therapy (ET) in women with breast cancer (BC) are 25%-50% and lead to inferior survival.  Understanding the effect of non-adherence on health outcomes is necessary to develop effective interventions.  This study examined real-world non-adherence and health outcomes among women using ET.  METHODS: Female respondents from the 2010-2012 U.S. National Health and Wellness Survey were included if reporting a diagnosis of BC and treatment with aromatase inhibitors (n=261), selective estrogen receptor modulators (n=113), or their combination (n=7).  The Morisky Medication Adherence Scale (MMAS-4 or MMAS-8, modified for use in oncology) was used to assess adherence, standardized using z-scores.  Descriptive analyses examined adherence, sociodemographics, and health behaviors.  Bivariate analyses compared health outcomes (quality of life, productivity, resource use) across adherent vs. non-adherent respondents. RESULTS: