Violent incidents in acute inpatient units for children and adolescents are a major and persistent problem. The demographic, clinical, and modifiable (environmental–organizational) risk factors that affect inpatient violence in an Acute Child and Adolescent Psychiatric Unit were investigated via a retrospective study. Data were collected from nursing and medical reports and the unit's census and included 100 days per year for 16 years. Incidents of violence and assault types were recorded, and variables such as the diagnostic category of assailants, total number of patients, and staffing factors during the incident were examined. Of the 2390 violent incidents recorded, 50% were attributed to cases of physical violence towards another patient, 17% to physical violence towards nursing staff, 19% to physical violence towards self and 14% to destruction of property. According to the final multivariable model, for each additional patient in the unit, the risk of a violent event increased by 9.51%; for each additional offender patient, the risk increased by 14.06%; the number of assistant nurses was associated with a 25.03% increased risk; and, after 2006, the risk increased by 68.99%. The most significant factor associated with a 59.98% decreased risk was the total number of nursing staff. All variables significantly and independently contributed to the model. Acute inpatient psychiatric units with a small number of hospitalized patients, adequate, well‐trained and specialized nursing staff, and the hospitalization of different types of patients in separate wards or units are expected to facilitate a reduction in the frequency of violent incidents.