PURPOSE: We determined the frequency of amygdalar-hippocampal atrophy in patients with congenital porencephaly-related seizure disorders to ascertain whether specific MR features of the porencephaly correlate with amygdalar- hippocampal atrophy and epilepsy. METHODS: We studied brain MR images of 22 patients with congenital porencephaly and measured the volume of the amygdala, the hippocampal formation, and the porencephalic cyst. We then compared imaging features with seizure symptoms. RESULTS: Porencephaly was unilateral in 20 patients and bilateral in two. Eighteen patients had cortical or subcortical cavitation and four had encephaloclastic changes (noncircumscribed parenchymal destruction associated with cystic components). The porencephaly was located in the middle cerebral artery territory in 12 patients, in the posterior cerebral artery in four, in the internal carotid artery in two, and in multiple vessels in four. The volume of the porencephalic cyst ranged from 1% to 32% of total intracranial volume (mean, 11%). Volumetry detected atrophy of the hippocampal formation in 21 cases (11 unilateral, 10 bilateral) and atrophy of the amygdala in 12 (nine unilateral, three bilateral). No correlation was found between size or location of the porencephaly and degree of hippocampal atrophy. Seizure symptoms correlated with mesial temporal origin but not with cyst location. CONCLUSION: Amygdalar-hippocampal atrophy often coexists with congenital porencephaly (95%), and the atrophy may be bilateral despite unilateral cysts. Hippocampal structures should be carefully assessed in patients with porencephaly-related seizures.