6605 Background: Adjuvant endocrine therapy for hormone receptor positive breast cancer is essential to decreasing recurrence and improving survival. However, adherence to these drugs has been reported to be suboptimal, the impact of which on breast cancer outcomes is unknown. Multiple non-modifiable risk factors have been associated with nonadherence. Identifying patients’ self-reported reasons for not taking these drugs as prescribed may be crucial to improving adherence. Methods: We obtained data from 49 women prescribed tamoxifen, letrozole, anastrozole, or exemestane for stage I-III invasive breast cancer. Written surveys were provided during the patients’ medical oncology visits. Our study collected demographic data on patient characteristics associated with nonadherence. Patients were asked to report reasons for missing doses including forgetting to take the drug, side effects, cost, and barriers to refill. Patients described their degree of adherence by identifying how often they miss a dose as never, once per month, once per week, or more than once per week. We compared their self-reported adherence to pharmacy refill records. Results: More than half the women (26 of 49) report regularly missing doses of their drug over the last year. Of these, 22 miss once per month, 3 miss once per week, and 1 misses more than once per week. Despite this, pharmacy records verified consistent refills in all 26 less adherent patients over the past year. The most common reason identified for missed doses (21 of 26) was forgetting to take the drug, followed by barriers to refill and side effects. 57% of all patients favored receiving an electronic reminder via text messaging or email. Nonadherence was associated with polypharmacy and lower levels of education, income, and activity. Conclusions: Our study provides insight into patient reported reasons for nonadherence to adjuvant endocrine therapy. Our patients reported forgetting to take their drug as most problematic. Patients’ self-reported adherence was confirmed (96%) by pharmacy records. Most patients are interested in an electronic reminder system via e-mail or text messaging, even if they report complete adherence. This has potential to be a cost effective intervention.