Clinicians assessing suicidal patients in emergency departments (EDs) must decide whether to admit the person to a psychiatric ward with voluntary or compulsory hospitalization or to discharge him/her as an outpatient. This cross-sectional study aimed to identify independent predictors of this decision among a large sample of self-harm (SH) patients. It used data from all patients admitted to four Swiss EDs between 2016 and 2019. Socio-demographic, clinical, and suicidal process-related characteristics data were evaluated against the decision for voluntary or compulsory hospitalization using t-tests, Chi-Square tests and logistic multiple regression. 2142 episodes from 1832 unique patients were evaluated. Independent predictors of decision to hospitalize included: male gender, advanced age, hospital location, depression and personality disorders, substance use, a difficult socio-economic condition, a clear intent to die, and a serious suicide attempt. Significant variables that emerged as independent predictors of compulsory hospitalization were hospital location, not having anxiety and personality disorders, being retired, having a clear intent to die, and making a serious suicide attempt. Hospital EDs had different rates of compulsory psychiatric admission. However, the decision to admit a patient for hospitalization, either voluntary or compulsory, was mainly based on clinical factors.