“South–South” partnerships forged between institutions in resource-constrained settings, usually in low- and middle-income countries, provide innovative frameworks for resource, knowledge, and expertise exchanges to address public health challenges in regions sharing similar contexts. Population-based cancer registries (PBCRs) and surveillance systems in low- and middle-income countries are essential for cancer control, yet they are scarce. In response, the authors formed a South–South Colombian–Mexican partnership to implement the first PBCR in Tijuana, northwestern Mexico, and an integrated pediatric cancer real-time clinical outcomes monitoring system, replicated from Colombia’s successful model, VIGICANCER. The newly established team assessed local needs in Mexico, adapted VIGICANCER protocols to the local context, and conducted training. In 2017, BajaREG was inaugurated in Tijuana, and, in 2018, joined the newly launched Mexican National Cancer Registry Network. In 2020, the Pediatric and Adolescent Cancer Registry Surveillance System (PACARSS) was integrated into BajaREG. Between 2018 and 2024, BajaREG registered 8 231 adult and 268 pediatric cases. PACARSS currently collects population-level data on pediatric cancer clinical outcomes in Tijuana. Despite multiple challenges, including the COVID-19 pandemic, stakeholder engagement enabled success. The authors showcase how locally tailored South–South partnerships can capitalize on collaborations and facilitate the implementation of sustainable PBCRs and surveillance systems in regions sharing similar challenges, resources, and health care systems.