PURPOSE: To assess the efficacy of functional hemispherectomy in promoting language acquisition in a child with severe language delay and continuous left hemispheric epileptiform discharge in the absence of clinical seizures. We report a 6-month-old girl who initially presented with a right hemiparesis secondary to a lesion of probable prenatal origin in the distribution of the left middle cerebral artery. Weeks later, she developed infantile spasms. At 1.5 years of age, because of intractable seizures, the patient had fenestration of the left porencephalic cyst and anterior temporal lobectomy. The seizures ceased; however, language development remained limited to 35 words at 3.5 years of age. The EEG showed almost continuous epileptiform activity over the left hemisphere with no independent epileptiform potentials contralaterally. She underwent a functional left hemispherectomy. METHODS: Imaging, electroencephalographic investigation, pre- and postoperative psychological and speech assessment were carried out. RESULTS: Considerable language, speech, and behavior improvement was noted within 2 months of surgery. CONCLUSIONS: Interictal epileptiform discharges can interfere with the development of contralateral hemispheric function in the absence of clinical seizures. Early functional hemispherectomy may have a role in promoting optimal language development in appropriately selected patients. Although the primary indication for functional hemispherectomy is to control intractable seizures, a secondary proposed indication is to reduce functional impairment of the other hemisphere by electrical interference.