Sexual offenders are at greater risk of nonsexual than sexual violence. Yet, only a handful of studies have examined the validity of risk assessments in predicting general, nonsexual violence in this population. This study examined the predictive validity of assessments completed using the Historical-Clinical-Risk Managment-20 Version 2 (HCR-20; Webster, Douglas, Eaves, & Hart, 1997), Short-Term Assessment of Risk and Treatability (START; Webster, Martin, Brink, Nicholls, & Desmarais, 2009), and Static-99R (Hanson & Thornton, 1999) in predicting institutional (nonsexual) aggression among 152 sexual offenders in a large secure forensic state hospital. Aggression data were gathered from institutional records over 90-day and 180-day follow-up periods. Results support the predictive validity of HCR-20 and START, and to a lesser extent, Static-99R assessments in predicting institutional aggression among patients detained or civilly committed pursuant to the sexually violent predator (SVP) law. In general, HCR-20 and START assessments demonstrated greater predictive validity—specifically, the HCR-20 Clinical subscale scores and START Vulnerability total scores—than Static-99R assessments across types of aggression and follow-up periods.