Abstract Purpose: To study the impact of comorbidities, multimorbidity, second primary cancers and socioeconomic determinants on adherence to follow-up recommendations for long-term breast cancer survivors (LTBCS), defined as women who survive 5 years or more after a primary breast cancer. Methods: We identified women diagnosed with breast cancer between 2000-2006 and followed-up between 2012-2016, including those with at least one contact with health services (n=2,078). Follow-up recommendations for LTBCS in Spain include 1 annual visit plus 1 image test. A woman was considered adherent with >50% of years with annual image test and visit throughout follow-up period. Multivariate logistic regression models were adjusted to determine the relationship between adherence and comorbidities and multimorbidity (2 or more chronic diseases) and other clinical and sociodemographic variables. A hierarchical cluster analysis was used to define specific multimorbidity clusters. A sensitivity analysis was conducted with mammogram as specific image test. Statistical significance was considered at 5% level. Results: Adherence to recommendations was 79.5% and 63.3% when considering mammograms only. We observed a higher adherence among LTBCS with multimorbidity, in those <70 years old, and with 5 to 9 years of survivorship. In the multivariate models, age under 40 years (OR=4.2; 95%CI: 2.3-7.6), a survivorship time between 5-9 years (OR=1.4; 95%CI: 1.1-1.8) and the metabolic and degenerative (OR=2.2 CI95%: 1.4-3.5) and thyroid disorders clusters (OR=2 IC95% 1.1-3.6) were associated with adherence. Similar results were observed in adjusted analyses by mammogram. In both analyses all multimorbidity clusters presented more adherence than LTBCS without chronic comorbidities. LTBCS with higher deprivation were found more adherent than LTBCS less deprived. Our results suggest a higher adherence among women experiencing second primary cancers, but the results were not statistically significant (OR=1.22; 95%CI: 0.8-2.0). Conclusion: There are differences in adherence according to age, survivorship time, and presence of multimorbidity. These results suggest a moderate adherence to the current follow-up recommendations for certain groups, making it necessary to adapt clinical practice guidelines considering the comorbidities and characteristics of the patients. Citation Format: Laia Domingo, David Abbad, Mercè Comas, Paula Santiá, Anna Jansana, Xavier Castells, Maria Sala. Impact of Multimorbidity on Adherence to Follow-Up Recommendations for Long-Term Breast Cancer Survivors [abstract]. In: Proceedings of the 11th Annual Symposium on Global Cancer Research; Closing the Research-to-Implementation Gap; 2023 Apr 4-6. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2023;32(6_Suppl):Abstract nr 49.