OBJECTIVE: An intervention to structure patient-key worker communication has been tested in a randomized controlled trial. The aim of this paper was to investigate effectiveness of the intervention in terms of moderators of effectiveness. METHOD: A total of 507 patients with schizophrenia were included. Moderators of effectiveness were investigated using two-way anovas. RESULTS: Patients with a better relationship with their key worker and a shorter duration of illness at baseline benefited more from the intervention in terms of quality of life. Patients who received the intervention who were in competitive employment or had a shorter duration of illness showed greater reduction of unmet needs. Older patients receiving the intervention had better treatment satisfaction. CONCLUSION: Outcome of the intervention was moderated by patient characteristics. Moreover, the moderating characteristics varied depending on the specific outcome. Evidence on moderators is very limited, even though, they are significant for understanding, targeting and implementing complex interventions.