High rates of mental illnesses and victimization have been reported for prison populations. This study estimates physical and sexual victimization rates (inmate-on-inmate and staff-on-inmate) for people with and without mental illnesses residing in Spanish prisons. A random sample of 2484 male and 225 female inmates was drawn from eight prisons in Spain. Self-report data were collected on victimization, mental illness and sociodemographic characteristics. Prevalence rates of physical and sexual victimization during the past six months in prison among men with mental illnesses were higher than for men without reported mental illnesses (39.1% vs. 16.4% and 8.6% vs. 3.3%, respectively). Similar comparative results were found for women with and without mental illnesses (29.7% vs. 17.5% and 13.3% vs. 10.3%, respectively). A positive association was found between mental illnesses and victimization. This evidence suggests the need for integrated trauma treatment and proactive steps to protect incarcerated persons from violence during incarceration.