Summary: All antiepileptic drugs may provoke positive or negative psychiatric reactions in individual patients. These psychotropic effects are not simply idiosyncratic but depend on the drug's anticonvulsive strength and the person's genetic and biographic psychiatric predisposition. Mechanisms related to psychiatric adverse events are polytherapy and folate deficiency, forced normalization, drug toxicity, and withdrawal. Our knowledge on dose independent, idiosyncratic psychotropic side effects is still limited. With respect to the older antiepileptic drugs there are almost no systematic data, and knowledge is largely empirical and based on anecdotal reports. With respect to the new generation of anticonvulsants there are data on psychiatric side effects from drug trials. However, these data are not always entirely transparent to the interested epileptologist. Moreover, drug trials are designed to test anticonvulsive efficacy and psychiatric adverse events are not systematically reported, thus severity psychopathologic nature of behavioral problems remain obscure. Differences in patients included in trials do not allow comparisons of psychiatric risks of specific drugs, particularly since following the vigabatrin experience, patients with a psychiatric history were often excluded from trials. In this chapter, methodological issues related to data on psychiatric adverse events of AED are discussed followed by an overview on the current knowledge on psychiatric side effect profiles of old and new antiepileptic drugs. Key Words: Antiepileptic drugs-Epilepsy-Side effects-Forced normalization-Positive psychotropic effectsThere are various parameters of interest in the context of psychiatric adverse events. (a) Drug-related incidence rates: how often and when in the course of treatment are complications to be expected when a specific drug is given? (b) Medication-related parameters: what are the differences between monotherapy and polytherapy? Is there a relationship with titration rates and maximal dosages? (c) Psychopathology and outcome of the psychiatric reaction: are there specific psychiatric syndromes? Is there a relationship with cognitive side effects? What is the prognosis? Which actions ought to be taken? (d) Neurologic, psychiatric, and epileptologic risk factors: how can we identify vulnerable patients?Diagnostic criteria for psychiatric side effects are neither standardized nor defined. The four major categories used in the literature are psychoses, affective syndromes, behavioral or personality disorders, and encephalopathies. From a nosologic point of view, these categories are not distinct and not specific, e.g., psychoses may be chronic and schizophrenia-like or transient and delirious. Many studies refer to isolated psychopathologic symptoms, such as nervousness, anxiety, or depressed mood. The clinical significance and the broader psychiatric conAddress correspondence and reprint requests to Bettina Schmitz at the Department of Neurology, Charitt, Humboldt Universitat, D-13353, Berlin, Germany. ...