Background: The association between multimorbidity and breast cancer is not yet fully understood. Few studies have published data on the association between multimorbidity and breast cancer in Africa, and none of them were conducted in Sudan. This study was conducted to estimate the prevalence and associated factors for multimorbidity (obesity, hypertension, diabetes, cardiovascular disease, asthma and tuberculosis, and HIV) and their association with breast cancer stage in women newly diagnosed with breast cancer in eastern Sudan. Methods: A retrospective cross -sectional study was conducted at East Oncology Center in Gadarif, eastern Sudan, from January to October 2021. Medical files were reviewed and sociodemographic, clinical data (comorbidities of hypertension, diabetes, cardiovascular disease, asthma, tuberculosis, and HIV) were retrieved. Logistics regression analysis was performed. Results: Medical files of 384 women who had newly diagnosed breast cancer were reviewed and included in this analysis. The median (interquartile) of their age was 50.0 (39.0‒60.0) years. Sixty-five women (16.9%) had multimorbidity. Obesity (77, 20.1%), hypertension (66, 17.20%), and diabetes mellitus (50, 13.0%) were the most common forms of morbidity among these women. Multivariate analysis showed that age was positively associated with multimorbidity (adjusted odds ratio [AOR] = 1.04, 95% confidence interval [CI] = 1.02‒1.07). Women with a lower level of education (AOR = 3.23, 95 % CI = 1.73‒6.04) and residing in urban areas (AOR = 2.22, 95% CI = 1.14‒4.34) were at higher risk for multimorbidity. Multivariate analysis showed that women with multimorbidity were at higher risk for presenting with newly diagnosed advanced breast cancer (AOR = 3.36, 95% CI = 1.85‒6.08). Conclusion: In eastern Sudan, older women, women with less education, and women residing in urban areas are at higher risk for multimorbidity associated with advanced newly diagnosed breast cancer.