summary  This study concerns a patient suffering from epilepsy and schizophrenia of the paranoid type, which is difficult to treat. The patient had been treated with lamotrigine, but administration of the drug was discontinued. We find a remarkable relationship between the time when the psychosis went into remission and the time positive symptoms re-emerged when the drug was discontinued. This time relationship is discussed in the light of two important considerations: lamotrigine is known to be a glutamate antagonist and schizophrenia is hypothesized to be hypoglutaminergic. On the basis of the pharmacodynamics and the published articles to which we refer, we advise caution in prescribing lamotrigine for patients who are known to suffer from psychotic disorders.