The ten French psychiatry high security care units (Unité pour Malades Difficiles : UMD) are the only forensic institutions in the country to provide care for dangerous and/or difficult patients (homicide, acts of barbarity, sexual assault, cannibalism, pyromania…). They benefit from intensive care protocols and high security measures. In this first epidemiological multicentric descriptive study in French history including 418 violent and homicidal patients, medico-judiciary and social characteristics of the standard UMD patient are described. This standard patient is a young single man, with a criminal record and from an underprivileged background, suffering from treatment-resistant schizophrenia with strong delusional symptoms. He has a weak compliance to treatment, low insight, a history of drug abuse and is admitted for severe violence against others and in particular against caretakers or for homicidal act. The study's secondary goal is to revisit the risk factors of high violence described in medical literature and to reveal new ones (cultural uprooting, parental psychopathology, homelessness, perverse sadistic behavior, aggressive behavior a month prior the violent acting out, resistance to antipsychotic drugs, treatment discontinuation), particularly in the homicidal patient cohort. This study should enable clinicians to evaluate dangerousness and to offer better medical care and preventive measures against violence.