People with learning disabilities are sometimes prescribed psychotropic medication to help manage their challenging behaviour. This case study describes how a multicomponent behavioural intervention in conjunction with the systematic withdrawal of sodium valproate was strongly correlated with reduced aggression. No symptoms of bipolar disorder or epilepsy were observed over the course of this 135-week case study. No aggression was observed during the last 20 weeks of the study. Aggressive behaviour as a possible side effect of sodium valproate should be considered in people with learning disabilities.