In an attempt to correlate neuropsychological deficits and various neurophysiological aspects of focal epileptic activity in benign childhood epilepsy, we have reviewed the findings of a longitudinal group study of benign childhood epilepsy with centrotemporal spikes (BCECTS) and several case studies of continuous spike-waves during slow sleep syndrome (CSWS). We first distinguish the temporary neuropsychological impairments often observed in the natural history of BCECTS from the more long-lasting and more specific neuropsychological deficits associated with CSWS, of which the Landau-Kleffner syndrome (LKS) is the most studied clinical form. A series of metabolic findings from (18)FDG-PET studies in BCECTS and CSWS children have shown that specific cognitive impairment is related to increased glucose uptake in cortical areas restricted to the associative cortex coincident with the focus of spike-wave discharges. From recent functional neuroimaging data of three patients recovered from LKS, we address the issue of the pathophysiology of cognitive impairment persisting after complete recovery of epilepsy. Finally, we discuss the reliability of the study of mismatch negativity to address the issue of the early effect of interictal discharges in typical and atypical BCECTS on the auditory cortex and the development of speech processing essential to verbal learning.