Valproic acid, a primary anticonvulsant drug, has recently been studied for purported effectiveness in disparate disorders of mood and behaviour. The psychopharmacological treatment of patients with acquired brain injury frequently includes numerous trials of psychotherapeutic drugs such as antipsychotics, benzodiazepines, antidepressants, and lithium, in an effort towards affective and behavioural improvement. In this report we describe and graphically depict the striking efficacy of valproic acid in reducing and improving destructive and aggressive behaviours in five patients with acquired brain injury. In all cases valproic acid was effective after other pharmacological interventions were not. Also, the addition of valproic acid was followed by neurobehavioural improvement rather quickly, often within 1-2 weeks. Advantages of valproic acid, in addition to its possible unique efficacy, include a lower propensity towards sedation and cognitive impairment, and thus a more robust potential for rehabilitation participation. Behaviours associated with affective disorders ranging along the affective spectrum from depression to dysphoric mania may be particularly amenable to valproic acid. The drug may also be beneficial in some cases in which another psychotropic anticonvulsant, carbamazepine, was not.