Background: Patient safety is a core dimension of healthcare quality and has become a global priority. According to the report by the U.S. Institute of Medicine, between 44,000 and 98,000 deaths occur annually due to medical errors in hospitals. One of the key indicators of patient safety is the Adverse Events (AE), defined as unintended harm to a patient that results from medical care rather than from the underlying disease. The assessment of adverse events is not only a tool for detecting errors but also an active strategy for improving system reliability and safety. Accurate identification of adverse events is therefore essential for enhancing patient safety and serves as a critical performance indicator with financial implications for hospitals. Aim: To determine the incidence of adverse events in referral hospitals and to analyze the relationship between triggers and adverse events. Material and Methods: Data were collected during 2023–2024 from three referral hospitals, the First, Second, and Third State Central Hospitals after obtaining institutional approval. The study was conducted within the framework of the Whole System Measures methodology developed by the Institute for Healthcare Improvement (IHI), which is internationally used for system-wide performance assessment. Data extraction was performed from electronic health records and inpatient departments, and statistical analyses were conducted using SPSS version 25. Results: The study identified 8.3% adverse events per 1,000 patient-days, which is 1.66 times higher than the international reference rate. A statistically significant association was observed between the number of triggers and the occurrence of adverse events, indicating that the use of triggers facilitates the active detection of adverse events. Conclusion The incidence of adverse events in tertiary specialized hospitals was found to be higher than international benchmarks. The application of trigger-based active surveillance proved to be an effective method for identifying adverse events and enhancing patient safety monitoring systems.