Antipsychotic agents, most often used for treatment of schizophrenia, are sometimes prescribed for the agitated patient with an organic brain disorder. We report the case of a brain-injured patient who was prescribed chlorpromazine for agitation and who developed a delusional state while taking this antipsychotic agent. The emergence of this delusional state coincided with the exacerbation of certain cognitive deficits. Possible mechanisms for this phenomenon are discussed. Caution is advised when prescribing neuroleptics for patients with traumatic brain injury, especially those agents with significant cognitive side-effects or with a significant potential to precipitate seizures.