Objective : The efficacy, tolerability and safety of quetiapine in schizophrenia patients diagnosed by the diagnostic criteria of schizophrenia of the Diagnostic Statistical Manual 4th edition was studied in psychiatric department of 4 hospital in Korea. Methods : Sixty-four patients (male 31, female 33 : age 34.2±10.4 years: illness duration 8.1±8.3 years) who showed acute exacerbation. pm1ial response, or intolerable adverse event to previous antipsychotic drugs were recruited. Doses of quetiapine were adjusted to maximize efficacy and minimize adverse events. Efficacy was assessed by the Brief Psychiatric Rating Scale (BPRS) and Clinical Global Impression (CGI) scale. Tolerability and safety were assessed by reports of adverse events. clinically significant abnonnal laboratory values and changes from the baseline to week 8 in the Abnonnallnvoluntary Movement Scale (AIMS) and Simpson-Angus total score as index of extrapyramidal symptoms (EPS). Results : Fiftythree patients completed the 8 weeks trial. The clinical symptoms indexed by BPRS were significantly improved (baseline score=37.9±13.0. score at the end=24.3±13.6 : F=41.5. d.f.=2.4. p=0.000). The CGI score of severity of illness was also significantly reduced (baseline score=4.7±1.1. score at the end= 3.6±1.2 : F=27.6, d.f.=2.2, p=0.000. The frequencies of the worsening of AIMS and Simpson-Angus scores at the end of study were 7.5% and 4.2%, respectively. The most common adverse events of at least moderate intensity were EPS (9.3%). Constipation (6.3%). and sedation (4.7%). Conclusion : The results of this study suggest that quetiapine is effective, may have a favorable EPS, and has overall safe tolerability in the patients with schizophrenia, and schizophreniform disorder.