With the introduction of several new anticonvulsant drugs into clinical practice in recent years, renewed attention has been paid to treatment-emergent effects, especially behavioural syndromes. In this review, the more severe psychiatric syndromes that may be associated with anticonvulsants are discussed, especially personality disorders, affective syndromes and psychoses. The important concept of forced normalisation is discussed, and its clinical counterpart, alternative psychosis. Affective disorders and psychoses have been described as associated with most of the new anticonvulsant agents, and they are often seen in a setting in which previously intractable patients suddenly become seizure free. Other cases may relate to intoxication, the precipitation of a status epilepticus, or ensue as part of the background frequency of those syndromes that are seen in epilepsy irrespective of medication.