Hallucinosis is a dreamlike state that can occur as a result of a vascular lesion located in the brainstem. A patient experienced this type of hallucinosis characterized by a rich dreamlike episode during a stroke. The relation of this acute hallucination to the emergence of dreams of the same theme during psychotherapy was studied using the psychoanalytic method. The common themes binding the content of the dream and the hallucination together highlight the value of the free-association technique in the study of the neurological mechanisms implicated in dream genesis and dream work.