This study was conducted using prospective methods to analyze predictions of the risk of physical aggression from patients with a mental illness and the variables used in these predictions. A total of 252 individuals participated in the study, all of whom were inpatients in acute psychiatric wards. Data were collected using a questionnaire consisting of two questions designed to determine the nature of predictions of the risk of physical aggression from mental health patients at admission and the variables used to make these predictions. Descriptive statistics and χ2‐tests were used for the data analysis. For approximately two thirds of the patients (61.9%, n = 156), a low‐level risk was predicted. The rate of patients predicted to demonstrate physical aggression was significantly higher. Nurses were better able to predict non‐aggressive behavior than risks of aggressive behavior. To improve the accuracy of predicting which patients with a mental illness will show aggressive behavior, a risk assessment should be conducted during hospitalization. Using a person‐centered approach, administrators in psychiatric settings should adopt an integrative perspective, considering individual and environmental factors, via a multi‐disciplinary approach.