The syndrome of malignant migrating partial seizures in infancy was first reported in 1995, and is now included among the childhood epilepsy syndromes in development in the proposal of the revision of the International League Against Epilepsy (ILAE) classification of the epilepsies and epilepsy syndromes. The main clinical features are seizure onset in the first 6 months of life, occurrence of almost continuous migrating polymorphous focal seizures, combined with multifocal ictal electroencephalography (EEG) discharges, and progressive deterioration of psychomotor development. Etiology is so far unknown. Seizures are markedly drug resistant and outcome is generally severe. Based on age at onset, migrating partial seizures in infancy (MMPEI) may be placed between early epileptic encephalopathies (early myoclonic encephalopathy [EME] and early infantile epileptic encephalopathy [EIEE]) and infantile spasms.