The purpose of this study is to measure the incidence of seclusion, identify possible determinants of seclusion and to gain insight into the use of antipsychotics before and after seclusion in acutely admitted patients. In The Netherlands, special treatment methods including seclusion and involuntary medication may only be applied in involuntarily hospitalized patients in cases of danger to the patient or others, with exclusion of emergencies. Data were retrospectively collected over the years 1997-1999 from a consecutive sample of 996 patients hospitalized on adult psychiatric admission wards. Young age, low Global Assessment of Functioning score, involuntary hospitalization and manic episode were significantly associated with seclusion, applied in 28.6% of the patients. The median time from admission to seclusion among psychotic patients who used antipsychotics during the first week was 7 days. In patients not using antipsychotics this was 2.5 days. In a substantial proportion of the psychotic patients antipsychotic treatment was initiated during or shortly after seclusion with a two times higher risk on antipsychotics in secluded patients compared with non-secluded patients (relative risk: 2; 95% confidence interval: 1.2-3.4). It was concluded that the use of antipsychotics is associated with a later application of seclusion. In a substantial proportion of the patients, treatment with antipsychotics was initiated during or shortly after seclusion.