This study reported on the efficacy of Reciprocal Skills Training (RST), a family-based treatment modality for childhood externalising disorders. Children (N = 57) ranging from 7 to 12 years old who fulfilled diagnostic criteria for oppositional defiant disorder were randomly allocated to RST (in either a hospital or clinical setting) or a waiting-list control group. At posttreatment, no significant differences were observed across the two treatment settings. Results indicated that 95.5% of children in the hospital setting and 72.2% of children in the clinical setting no longer met criteria for oppositional defiant disorder, compared to 30% of children on the waiting list. Children in the treatment groups also obtained significantly lower scores on the Externalising scale of the Child Behaviour Checklist, compared to the waiting-list group. In addition, mothers' levels of stress and depression were significantly reduced at posttreatment, compared to mothers of children on the waiting list. These findings suggest that RST is an effective treatment modality for children displaying externalising behaviours, as well as for their mothers. The results are discussed in terms of limitations of the current study and future directions for research and clinical practice.