Phase 1 of the Clinical Antipsychotic Trials of Intervention Effectiveness (CATIE) study enrolled a sample of 1493 chronic schizophrenia patients. The European First Episode Schizophrenia Trial (EUFEST) enrolled 498 patients. We have combined these two samples to study the effects of hostility on study discontinuation as well as to examine correlates and predictors of hostility. Individual data from 1154 patients with complete data were used for analyses. Survival analysis demonstrated that higher hostility was associated with earlier all-cause treatment discontinuation. Furthermore, regression analysis indicated that increased hostility was associated with more severe positive symptoms, lower adherence to pharmacological treatment, younger age, impaired insight, and more drug or alcohol consumption. The clinical implications of the results point to the importance of establishing therapeutic alliance while managing patient's symptoms of hostility with antipsychotics such as olanzapine combined with psychosocial interventions to improve insight and reduce substance use.