Some aggressive incidents in psychiatric wards result in seclusion, whereas others do not. We used the Staff Observation Aggression Scale-Revised and the mental health trust's database to identify determinants that predicted seclusion after aggression. These consisted of demographic, diagnostic, contextual, and aggression characteristics and were analyzed in a multilevel logistic regression. This showed associations between seclusion and aggression for the following: younger age, involuntary status, history of previous aggression, physical or dangerous violence, aggression being directed against objects, and a more severe incident. Thus, seclusion after aggression appears to be mainly predicted by aggression itself.