IMPORTANCE: Although many studies have explored the correlates of violence during first-episode psychosis (FEP), most have simply compared violent psychotic individuals with nonviolent psychotic individuals. Accumulating evidence suggests there may be subgroups within psychosis, differing in terms of developmental processes and proximal factors associated with violent behavior. OBJECTIVE: To determine whether there are subgroups of psychotic individuals characterized by different developmental trajectories to violent behavior. DESIGN, SETTING, AND PARTICIPANTS: The National EDEN (Evaluating the Development and Impact of Early Intervention Services in the West Midlands) Study longitudinal cohort assessed premorbid delinquency (premorbid adjustment adaptation subscale across childhood and adolescence), age at illness onset, duration of untreated psychosis, past drug use, positive symptoms, and violent behavior. Group trajectories of premorbid delinquency were estimated using latent class growth analysis, and associations with violent behavior were quantified. This study included 6 early intervention services in 5 geographical locations across England, with violent behavior information available for 670 first-episode psychosis cases. MAIN OUTCOMES AND MEASURES: Violent behavior at 6 or 12 months following early intervention services entry. RESULTS: Four groups of premorbid delinquency were identified: stable low, adolescent-onset high to moderate, stable moderate, and stable high. Logistic regression analysis, with stable low delinquency as the reference group, demonstrated that moderate (odds ratio, 1.97;95% CI, 1.12-3.46) and high (odds ratio, 3.53;95%CI, 1.85-6.73) premorbid delinquency trajectories increased the risk for violent behavior during FEP. After controlling for confounders, path analysis demonstrated that the increased risk for violence in the moderate delinquency group was indirect (ie, partially mediated by positive symptoms) (probit coefficient [β] = 0.12; P =.002); while stable high delinquency directly increased the risk for violence (β = 0.38; P =.05). CONCLUSIONS AND RELEVANCE: There appear to be diverse pathways to violent behavior during FEP. Stable high premorbid delinquency from childhood onwards appears to directly increase the risk for violent behavior, independent of psychosis-related risk factors. In addition to tackling illness-related risks, treatments should directly address antisocial traits as a potent risk for violence during FEP. © 2013 American Medical Association. All rights reserved.