Background: Breast cancer (BC) is the most common cause of cancer-related death and morbidity among young women in Latin America. This group has a higher prevalence of advanced disease stages at diagnosis compared to their older counterparts. Thus, strategies aimed at detecting BC at early stages are imperative. Breast self-examination (BSE) remains a useful strategy for BC detection, especially in women who do not routinely undergo screening with imaging studies. This study aims to evaluate factors related with BSE practice in Mexican young women with BC and assess its association with earlier disease stages. Methods: Women aged ≤40 newly diagnosed with BC from 2014 to 2020 at three cancer referral centers in Mexico accrued in the Joven & Fuerte cohort were included and asked to complete a socio-demographic survey. Fisher’s exact and Mann-Whitney U tests were used to evaluate associations between BSE and socio-demographic characteristics, as well as disease stages. Results: A total of 554 patients with a median age at diagnosis of 36 years (range: 19-40) were analyzed. Most patients (65%) were married or in a domestic partnership, and the majority were housewives (63%). Regarding educational background, 64% had completed at least high school, and up to 84% had a monthly income < 11,600 Mexican pesos (US$ 581). Overall, 85% of patients had public insurance, 6% had private insurance, and 9% were uninsured. The distribution of clinical stages at diagnosis was: 0 (2%), I (11%), II (45%), III (32%), and IV (10%). BC detection methods were: 85% by self/partner exam, 11% by an imaging study, and 4% by a healthcare professional. A total of 443 (80%) patients practiced BSE, of which 50% did it on a monthly basis, 18% every 2-3 months, and the remaining 12% every 4-12 months. Notably, a higher educational level (≥ high school v ≤ middle school) was positively associated with BSE practice (RR: 1.28; 95%CI 1.06-1.54; p= 0.005). No significant association was found between BSE and age (≤35 v> 35), marital status (in a relationship v no), occupation (housewive v other), monthly income ( < 11,600 v≥11,600) or medical coverage (public/uninsured v private). Patients that performed BSE were more likely to be diagnosed with early BC (stages 0-II) compared to those that did not (61% v 45%; p= 0.003). No association was found between BSE frequency and stage at diagnosis. Noteworthy, patients with private insurance were more likely to be diagnosed with stages 0-II compared to those with public or no insurance (80% v 56%; p= 0.007). Conclusions: The significant association between BSE and earlier stages at diagnosis found in this study highlights the need to raise awareness and promote this practice among young women with the objective of downstaging BC diagnoses. Public health interventions such as educational and social media campaigns that aim to improve the correct practice of BSE might be particularly useful in settings with inadequate screening programs.