Abstract Background: Sexual dysfunction is a common health problem in women, and it can occur during breast cancer treatment and survivorship. This study aims to determine the frequency of sexual disfunction among Brazilian women with early breast cancer on adjuvant endocrine therapy and to explore its relationships with patients’ clinical and social characteristics, adherence to ET, quality of life, return to work and healthcare insurance. Methodology: Women with history of early-stage ER+ invasive carcinoma of the breast on adjuvant endocrine therapy for at least 6 months were invited to participate of this study. Sexual dysfunction was evaluated using the Female Sexual Function Index questionnaire (FSFI). A score of < 26.55 in FSFI indicates sexual dysfunction. We evaluated sexually active patients (women should have at least one sexual intercourse in the previous four weeks). Demographic and medical information, site of treatment (private versus public), degree of education (completed high school vs not) were reviewed from medical records. Quality of life was assessed using EORTC QLQ C30 and BR-23 forms and adherence to ET was assessed by the Morisky Medication Adherence Scale (MMAS-8). Additionally, patients were interviewed about return to work. Data collection was performed using RedCap software and statistical analyzes were performed on the software R (R Core Team (2022). Qualitative variables were compared between groups using the Chi-square or exact Chi-square test and for quantitative variables the non-parametric Mann-Whitney test was used. Multivariable analysis was performed using Poisson regression. P < 0.05 was considered significant. Analyzes were performed in SAS 9.4. Results: From June 2021 to May 2023, a total of 461 women with ER+ early-stage breast cancer from 12 Brazilian institutions were included in this analysis. The mean age was 56.0 years (range 22-93 ), 47.7% were non-white and 38.7% were premenopausal. A total of 233 women (50.6%) had private insurance and the remaining were treated in public institutions. Median duration of ET use was 2.78 years (range 6 months- 9.61 years).Only 249 (54%) out of 461 patients who accepted to participate in this study declared to have sexual intercourse in the previous 4 weeks before evaluation and composes the population of this analysis. Sexual disfunction according results of FSFI questionnaire was found in 113 (53.3%) participants. Age was significantly associated with sexual dysfunction with women > 40 years-old having higher rates (95.3%) compared with versus younger patients (4.71% p=0.0069). Patients without sexual dysfunction had significantly higher EORTC QLQ C30 Global health status, Physical Functioning, Emotional Functioning, Sexual Functioning and Sexual Enjoyment scores than those with sexual dysfunction (p = 0.0060, p = 0.0242, p = 0 .0353, p = 0.0002 and p < 0.0001 respectively). ET duration between 2 and 5 years vs < 2 years, higher vs lower education level, EORTC QLQ-BR23 breast symptom and sexual functioning higher scores were significantly associated with the occurrence of sexual dysfunction in multivariated analysis (p < 0.05). Conclusion: In our study, only 54% of women evaluated had sexual intercourse in the previous four weeks and from those women 53.3% reported sexual dysfunction. Factors related to sexual dysfunction were higher education level, ET duration between 2 and 5 years, breast symptom and sexual functioning higher scores. div style=margin-top:10px; margin-bottom:20px;>Characteristic with adjusted prevalence ratios for the occurrence of sexual disfunction XX XX PR: prevalence ratio, EORTC: European Organisation for Research and Treatment of Cancer Citation Format: Daniele Assad-Suzuki, Fernanda Moura, Danielle Santos, Sulene Oliveira, Cristiano Souza, Heloísa Resende, Andrea Shimada, Anna Luiza Galvão, Bruno Souza, Amanda Castro, Monalisa Andrade, Yuri Beckedorff, Maria Cristina Magalhães, Carlos Paiva, Angelica Rodrigues, Daniela Pereira, Daniela Rosa, Romualdo Barroso-Sousa. Sexual dysfunction among Brazilian women with early breast cancer on adjuvant endocrine therapy (ET) [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO3-11-05.