Abstract: Background: Victimization is associated with worse social and clinical outcomes of individuals with severe mental illness (SMI). A relapse of SMI may be one of the clinical consequences of assaultive trauma. As far as we know, there is no published study that analyzes nationwide health registers to assess the risk of SMI rehospitalization following assault. Aim: We aimed to assess whether exposure to assault is associated with an increased risk of psychiatric hospitalization in those with SMI. Methods: We utilized data from the Czech nationwide registers of all-cause hospitalizations and all-cause deaths. We defined exposed individuals as those discharged from a hospitalization for SMI between 2002 and 2007, and hospitalized for serious injuries sustained in an assault in the subsequent 7 years. For each assaulted individual, we randomly selected five counterparts, matched on SMI diagnosis, age and sex, who were not assaulted in the examined time period. We used mixed effect logistic regression to assess the effect of assault on the risk of SMI rehospitalization within the following 6 months. We fitted unadjusted models and models adjusted for the number of previous SMI hospitalizations and drug use disorders. Results: The sample consisted of 248 exposed and 1 240 unexposed individuals. In the unadjusted model, assaulted individuals were almost four times more likely to be rehospitalized than their non-assaulted counterparts (odds ratio (OR) = 3.96; 95% CI 2.75; 5.71). After adjusting for all covariates, the OR remained threefold higher (OR = 3.07; 95% CI 2.10; 4.49). Conclusion: People with a history of SMI hospitalization were approximately three times more likely to be rehospitalized for SMI within 6 months after an assault than their non-assaulted SMI counterparts. Soon after a person with SMI is physically assaulted, there should be a psychiatric evaluation and a close follow-up.