This article draws on a prospective longitudinal study in which Assertive Community Treatment (ACT) model fidelity and patient outcomes were assessed in twenty outpatient treatment teams. 530 severely mentally ill patients participated in the study. Delinquency outcomes were assessed three times during a two-year follow-up period. At baseline, 49% of the patients had a recent criminal history, meaning that they had at least one reported contact with the police and/or the justice system in the past year. Patients with a recent criminal history had more serious psychosocial problems at baseline compared to those without a recent criminal history. Delinquency outcomes showed improvement over time, but this was not associated with ACT model fidelity. The study shows an association for homelessness and criminal activity. The persistent criminal activities of some of the patients showed that for this group extra interventions are needed that specifically target reduction of criminal behavior.