Isolation for infection prevention and control, albeit necessary, may result in unintended consequences for patients (e.g., less attention, suboptimal documentation and communication, higher risk of preventable adverse events [AEs]). This prospective cohort study found that the incidence of all AEs and preventable AEs were significantly higher in isolated patients compared to non-isolated patients, primarily caused by healthcare-associated infections. These findings highlight the importance of training and safety culture when providing care to patients in isolation, particularly given the expanded use of isolation due to the COVID-19 pandemic.