Background: To gain more insight into the antecedent factors of restraint in institutionalised people with intellectual disability (ID), the role played by several demographic and psychological client variables was investigated. Methods: The data of 475 people (age range 12-95 years) who were residents in a Dutch institution for people with ID were collected. The severity of restraint was rated on an ordinal scale. Results: None of the demographic variables height, weight, age, or length of stay were related to the application of restraint. Significant predictors were the psychological variables: low adaptive functioning, the presence of challenging behaviours, and a relatively high intellectual level. Of the challenging behaviours, specifically behaviours other than actual aggressiveness proved to be predictors of restraint. Conclusions: The fact that actual aggressiveness plays a minor role in predicting restraint is a new finding and should be further examined in future research. (Contains 4 tables.)