The majority of women treated for primary breast cancer (BC) will receive adjuvant endocrine treatment (AET). A treatment, which has several side effects with a varying degree of severity. In some cases, they result in impaired quality of life of the breast cancer survivors (BCS). For younger BCS, these side effects are often augmented by the fact, that premenopausal women may turn postmenopausal by the adjuvant chemotherapy. Among the most common side effects are hot flashes, sweating, vaginal dryness and arthralgia. Sexual problems are also common; however, sexual dysfunction (SD), defined as impairments in sexual function causing personal distress, are inadequately described among BCS on AET. Hence, SD may be underreported in both clinical studies and the daily clinic. The primary aim of this study was to estimate the prevalence of clinically relevant SD and to identify possible predictors of SD among BCS on AET. We conducted a cross-sectional survey among BCS who have been treated with AET's for more than 3 months, with no actual signs of recurrent disease and no previous cancer diagnosis. The survey consisted of questions regarding demographic factors, present and previous symptoms. The following validated questionnaires were used: Female Sexual Function Index (FSFI), Sexual Complaint Screener - Women (SCS-W), Beck Depression Inventory (BDI), International Consultation on Incontinence Modular Questionnaire - Female Sexual Matters associated with Lower Urinary Tract Symptoms (ICIQ-FLUTSsex) and subscales of the Cancer Rehabilitation Evaluation System (CARES). Additionally, data concerning tumor characteristics and cancer treatment were collected from the medical records. In total, 333 women with a mean age of 58.7 years were included in the study, of which 227 were sexually active. All were heterosexual. In the entire cohort, the most prevalent impairments were low libido (54%), anorgasmia (26%) and lack of arousal (25%). Although dyspareunia was the least frequent impairment reported by BCS (21%), it was the most distressing symptom. Urogenital symptoms were common with 47% of the women reporting vaginal dryness and 38% reporting pain with sexual intercourse. The sexually active BCS were younger, more often partnered, and more satisfied with their sexual life before the cancer diagnosis than those women being sexually inactive. Among the 227 sexually active women, 134 (59%) qualified for having SD. Of these 134 women, 78 (58%) perceived the cancer treatment as the primary reason for their sexual problems. In a multivariate analysis, the risk of having SD was significantly associated with experiencing more vaginal dryness and less psychological well-being. Whereas age, relationship satisfaction and duration of AET were not significantly associated with the risk of having SD. In conclusion, SD was highly prevalent among sexually active BCS on AET and was perceived as a long-term side effect of BC treatment by two thirds of BCS with SD. Vaginal dryness was the strongest predictor of SD. Of note, age was not related to neither prevalence of SD nor the degree of distress caused by the impairments. Hence sexual health is an important topic for BCS and should be addressed by the clinicians at follow up visits of BCS independent of their age. Citation Format: Mia F Andersen, Astrid Højgaard, Charlotte B Rotboel, Anders Bonde Jensen. Sexual dysfunction among breast cancer survivors in adjuvant endocrine treatment [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P2-13-14.