Compulsory admission (CA) refers to the process of hospitalization of an individual to a psychiatric ward or hospital, without their consent, due to severe mental health conditions. While it is an established and legally framed practice in many countries, it raises a number of ethical issues in terms of personal liberty and risks of potential misuse. Ethnicity, male gender and psychosis are the main risk factors for compulsory admission to psychiatric wards/hospitals in general population. Previous studies documented that CA is even more frequently used in prison, yet its determinants are still unknown. To address this issue, we explored the clinical, demographic and criminological determinants of compulsory admission in 317 detainees admitted to a psychiatric acute care secure ward located in the central prison of Geneva. We distinguished three groups: voluntary admissions only (VA), CA only and mixed admissions (MA). Judicial status and types of offenses were also recorded. Sociodemographic data included age, gender, and origin. Clinical parameters included previous compulsory admissions, previous hospital stays, number of admissions, length of stay, number of suicide attempts, short-term seclusions and ICD-10 clinical diagnoses. Fisher's exact, Chi