Objective: Agitation, aggression, and violence are increased in psychotic disorders. Additionally, an earlier age at onset may be associated with aggressive behavior. However, the relationship of age at onset, an agitatedaggressive syndrome as measured with the Positive And Negative Syndrome Scale for Schizophrenia -Excited Component (PANSS-EC), and its potential correlates in first-episode psychosis (FEP) has not been studied. Method: This study assessed the association between age at onset, an agitated-aggressive syndrome, and its potential correlates in a prospective sample of 52 FEP patients with early-onset and adult-onset followed up for 12 months. Results: Twenty-six patients conformed to the criteria of early-onset psychosis. Early age at onset was associated with antisocial personality disorder (p = 0.004; phi(c) = 0.39), a history of legal involvement (p = 0.005; phi(c) = 0.39), and higher rates of lifetime substance use disorder (SUD; p = 0.002; phi(c) = 0.42). Early-onset patients had significantly higher PANSS-EC scores over the course of observation (F(1,44.4) = 5.39; p = 0.025; d = 0.656), but no significant group differences emerged for the remaining PANSS subscores. PANSS-EC scores were correlated positively with antisocial personality disorder and forensic history at 6 weeks, 3 months, 6 months, and 12 months, and with lifetime substance use disorder at 3 months and 6 months. Conclusions: Patientswith early onset psychosismay have increased levels of agitation/aggressiveness, and, more likely, antisocial personality disorder, forensic history, and lifetime substance use disorder. These variables were linked to suicidality, aggressiveness, and involuntary treatment. (C) 2016 Elsevier B. V. All rights reserved.