Objective. Many patients with schizophrenia are not treated in line with evidence-based guidelines. This study examines the large-scale implementation of the National Multidisciplinary Guideline for schizophrenia in the Netherlands. Design. Observational, prospective study, with repeated measurement. Setting. Thirty mental healthcare teams in different regions of the Netherlands. Participants. Three hundred and fifty-nine clinicians with different professional backgrounds and 1489 patients suffering from schizophrenia. Intervention(s). Six evidence-based interventions for schizophrenia were implemented, in the context of a quality improvement collaborative: assertive community treatment (ACT) or its adapted version functional assertive community treatment (FACT), cognitive behavioural therapy, psycho-education, family interventions, individual placement support and pharmacotherapy. Main Outcome Measure(s). Professional performance, social functioning and relapse rates. Results. Improved professional performance, in line with guidelines. Availability of (F)ACT improved from 23 to 60%. Individual Placement Support improved from 20 to 53%. Complete care plans were composed for 38% of the patients and routine outcome monitoring was introduced in most teams. Social functioning improved slightly (HoNOS mean: from 6.2 to 5.6). Relapse rates did not improve during the course of the study. Conclusions. An intensive implementation programme can result in an improved delivery of evidence-based care, increased continuity of care and slightly improved outcomes for individuals with schizophrenia. More rigorous research designs have to confirm these findings. © The Author 2013. Published by Oxford University Press in association with the International Society for Quality in Health Care; all rights reserved.