Comparison of seclusion figures between wards in Dutch psychiatric hospitals showed substantial differences in number and duration of seclusions. In the opinion of nurses and ward managers, these differences may predominantly be explained by differences in patient characteristics, as these are expected to have a large impact on these seclusion rates. Nurses assume more admissions of severely ill patients are related to higher seclusion rates. In order to test this hypothesis, we investigated differences in patient and background characteristics of 718 secluded patients over 5,097 admissions on 29 different admission wards over seven Dutch psychiatric hospitals. We performed an extreme group analysis to explore the relationship between patient and ward characteristics and the wards' number of seclusion hours per 1,000 admission hours. In a multivariate and a multilevel analysis, various characteristics turned out to be related to the number of seclusion hours per 1,000 admission hours as well as to the likelihood of a patient being secluded, confirming the nurses assumptions. The extreme group analysis showed that seclusion rates depended on both patient and ward characteristics. A multivariate and multilevel analyses revealed that differences in seclusion hours between wards could partially be explained by ward size next to patient characteristics. However, the largest deal of the difference between wards in seclusion rates could not be explained by characteristics measured in this study. We concluded ward policy and adequate staffing may, in particular on smaller wards, be key issues in reduction of seclusion. © 2012 Springer Science+Business Media, LLC.