Previously, many patients with severe mental illness had difficulties to engage with fragmented mental health services, thus not receiving care. In a Dutch city, Assertive Community Treatment (ACT) was introduced to cater specifically for this group of patients. In a pre-post comparison, changes in mental health care consumption were examined. All mental health care contacts, ACT and non-ACT, of patients in the newly started ACT-teams were extracted from the regional Psychiatric Case Register. Analyses of mental health care usage were performed comparing the period before ACT introduction with the period thereafter. After the introduction of ACT, mental health care use increased in this group of patients, although not all patients remained under the care of ACT teams. ACT may succeed in delivering more mental health care to patients with severe mental illness and treatment needs who previously had difficulties engaging with fragmented mental health care services.