Three boys with hemimegalencephaly are reported. Two suffered neonatal convulsions and the third presented with seizures at seven months. In each case the EEG was grossly abnormal, with spike and wave activity. All three have significant developmental delay and demonstrate other manifestations of the condition: macrocephaly in two, contralateral hemiparesis in one and one boy has ipsilateral facial hemihypertrophy and linear naevus. Hemimegalencephaly can be recognised on cranial ultrasonography, and the seizures may respond to benzodiazepine therapy.