The aim of the study was to evaluate the adherence and efficacy of quetiapine treatment in a 6-month, multicentre, noninterventional naturalistic design. Overall, 710 schizophrenia patients using quetiapine or who had switched to quetiapine were included. The continuation rate for quetiapine treatment during 6-month follow-up period was 69%. Adherence improved with each subsequent visit for continued patients, 92.9% at the second visit to 96.1% at the last. Treatment adherence was correlated to improvement of symptoms, though not significantly. Patients having lower clinical global impression severity scores at the beginning were twice as likely to improve compared with patients with higher clinical global impression scores. Schizophrenia patients with antisocial behaviour problems had two and a half times higher drop-out rates. In conclusion, this naturalistic study showed that adherence to quetiapine treatment was high, and treatment was effective in schizophrenia patients during long-term treatment. Remission of symptoms in schizophrenia is much related to severity of symptoms at baseline, treatment adherence and characteristics of patients such as antisocial behavioural patterns.