The surgical treatment of chronic epilepsies is increasing rapidly. A review of 279 surgical specimens of patients with chronic pharmaco-resistant epilepsies from the University of Bonn Medical Centre revealed specific histopathological findings in 89% of all well-preserved specimens. The most frequent focal lesions were low-grade brain tumours such as gangliogliomas, pilocytic astrocytomas and dysembryoplastic neuroepithelial tumours. Other common findings were glioneuronal and vascular malformations and Ammon's horn sclerosis. This suggests that chronic intractable epilepsies are frequently caused by structural alterations.