Although several variables have been reported to be associated with behavioural problems in foster children, few studies have sought to establish more precisely the extent to which these variables may explain problematic behaviour. The main aim of this study is to determine the extent to which certain variables may predict behavioural problems shown by foster children. Participants included 104 foster children and their respective foster families. Multiple linear regression analysis revealed that the following variables predict behavioural problems in foster children: impulsivity/attention deficit in the child, level of burden in the foster carers, rigid or authoritarian parental discipline, and criticism/rejection by the foster parents. The model explained 46% of the variance in behaviour problems, with the greatest predictive power (29%) corresponding to the variable ‘impulsivity/attention deficit’. The results show that impulsivity/attention deficit is the most powerful predictor of behavioural problems in foster children. This is consistent with the findings of various studies that have reported an association between a lack of inhibitory control and problematic behaviour.