Background and Hypothesis Cardiovascular diseases are a leading cause of morbidity and mortality in patients with Chronic Kidney Disease (CKD). Acute Kidney Injury (AKI) has been increasingly recognized as a potential exacerbating factor for cardiovascular events in these patients. The CKD-REIN study aims to explore the relationship between AKI and the risk of Major Adverse Cardiovascular Events (MACE) in a cohort of CKD patients. We hypothesize that AKI is a significant and independent predictor of MACE in patients with CKD, and that the severity of AKI correlates with the risk of subsequent cardiovascular events. Methods This prospective cohort study included 3033 adult CKD patients from 40 outpatient nephrology clinics in France. Patients were followed for a median of 5.2 years. AKI episodes were identified and staged based on the KDIGO-AKI criteria. Cardiovascular events, including myocardial infarction, stroke, heart failure hospitalization, and cardiovascular death, were systematically recorded. The association between AKI and MACE was analyzed using a multivariable Cox model, adjusting for confounders such as demographic characteristics, medical history, and baseline kidney function. Results During the follow-up, 530 patients experienced at least one episode of AKI. The cumulative incidence of MACE at 1 year post-AKI was 8.1%. Patients with AKI had a significantly increased risk of MACE, with an adjusted Hazard Ratio (HR) of 5.78 (P < 0.001). The risk was consistent across different MACE components and was independent of age, sex, CKD stage, or comorbidities. The risk of MACE was higher for more severe AKI stages and for AKI events requiring hospitalization or associated with incomplete renal recovery. Conclusion The findings of this study confirm that AKI is a significant independent predictor of MACE in CKD patients, demonstrating a strong severity-response relationship. These results underscore the importance of vigilant cardiovascular monitoring and preventive strategies in CKD patients following AKI episodes. Understanding the mechanisms linking AKI to cardiovascular outcomes is crucial for developing targeted interventions to mitigate these risks.