It is a matter of dispute whether or not recurrent epileptic seizures cause neuronal damage in the human brain. We approached this question by measuring the volumes of the amygdala, hippocampus and parahippocampal gyrus with magnetic resonance imaging in 15 controls, 13 unmedicated patients with newly diagnosed epilepsy and 16 patients with chronic drug-refractory epilepsy. In all patients, the seizure origin was in the temporal lobe region and the seizure aetiology was unknown. Newly diagnosed epilepsy patients with seizure lateralization on the left had increased hippocampal right-left difference (p < 0.01) and right/left ratio (p < 0.05) compared with controls. Patients with chronic epilepsy and lateralization on the left had increased hippocampal right-left difference (p < 0.05) and right/left ratio (p < 0.05) compared with controls. In this patient group, the volume of the left hippocampus was 16% smaller than in controls (p < 0.01). The rostral portion of the parahippocampal gyrus was 12% smaller than in controls (p < 0.01). In chronic epilepsy patients with lateralization on the right, we found a statistically non-significant decrease (13%) in the right hippocampal volume compared with controls. In this patient group, the amygdaloid right-left difference (p < 0.05) and right/left ratio (p < 0.05) were decreased compared with controls. The present cross-sectional study provides evidence that mild hippocampal damage is already present in the early stages of epilepsy. Hippocampal damage is more severe in patients with a long history of recurrent generalized seizures.(ABSTRACT TRUNCATED AT 250 WORDS)